Acanthocystis

Acanthocystis Carter, 1863 (ref. ID; 3691, 4745)

Actinopoda: Heliozoea (ref. ID; 4745)
Heliozoa: Centrohelida (ref. ID; 7658)

[ref. ID; 1618]
Spherical; siliceous scales arranged tangentially and radiating siliceous spines with pointed or bifurcated ends; nucleus eccentric; a distinct central granule in which the axial filaments terminate. (ref. ID; 1618)

[ref. ID; 1923]
Nucleus eccentric, generally a central corpuscle from which the axial filaments arise. Spicules of 2 kinds: siliceous in the form of plates and delicate radiating spines. (ref. ID; 1923)

[ref. ID; 4687]
The genus Acanthocystis contains unicellular, free-floating planktonic or benthonic living organisms which are common in freshwater but also found more rarely in marine habitats. They are covered all over with siliceous scales of mainly 2 types, which form a more or less flexible armour (periplast). Other generic characteristics are the absence of a distinct covering of gelatin or mucus, the possession of a centroplast at the very centre of the cell from which the granulated axopodia radiate and, therefore, an eccentrically placed nucleus (Rainer 1968). The morphology of the scales appears to be constant and is thus often used to distinguish the species, in addition to the general morphology of the cell itself. The fine structure of the scales is, for the most part, beyond the resolution of the light microscope, so that classification based on this feature was necessarily somewhat vague. A further difficulty in the taxonomy of the genus Acanthocystis is that the internal cell structure is largely unknown, except for A. aculeata, A. turfacea, A. erinaceoides, and some others (Bardele 1977). (ref. ID; 4687)

[ref. ID; 4745]
Diagnosis; Centrohelid heliozoeans with tangential plate-scales and radial spine-scales; spine-scales with cylindrical shaft, attached to the central part of a radially symmetric basal plate. (ref. ID; 4745)
Remarks; The genus Acanthocystis is a widespread genus, common in freshwater, but some members are reported from marine habitats. The genus was erected by Carter (1863), with the diagnosis included in the description of its type-species, A. turfacea. From this description the genus Acanthocystis was diagnosed to cover heliozoeans with tangential plate-scales and radial spine-scales (Penard 1904). Till 1960, all members of the genus Acanthocystis were supposed to bear spine-scales with as cylindrical shaft, attached to the centre of a circular basal plate. However, Petersen and Hansen (1960) described two other types of spine-scales respectively on Acanthocystis perpusilla and Acanthocystis erinaceoides. A. perpusilla has spine-scale with an eccentrically placed incised basal plate. A. erinaceoides has spine-scales with a membranous base with two lateral tapering wings and no basal plate. Subsequent electron microscopic investigations amply confirmed the existence of different types of spine-scales within the genus Acanthocystis (Siemensma 1981; Nicholls 1983; Durrschmidt 1985, 1987; Croome 1986). At least 46 acanthocystid species have been studied electron microscopically (Siemensma, in press). They all share a fairly uniform structure of the plate-scales, but differ much in the shape and structure of the spine-scales. Most of the species classified within the genus Acanthocystis as understood until now bear spine-scales with a membranous base of a more or less eccentrically attached incised basal plate. However, these species are not covered by the name Acanthocystis in its original sense, since Carter (1893) described the spine-scales of the type-species as "straight, hollow, of uniform breadth in the shaft, bifid or forked at the distal, and discoid at the proximal extremity". Therefore, the genus Acanthocystis has become a polymorphic group rather than a taxonomic group and a revision has become necessary. The intention to present all known heliozoeans in one key (Siemensma, in press) necessitates some changes in the generic classification of Acanthocystis. The re-classification is based on recent reports (Siemensma 1981; Nicholls 1983; Durrschmidt 1985, 1987) and the observations reported here. The genus Acanthocystis is retained for species having spine-scales with a discoid, radial symmetrical basal plate. Species having spine-scales with a bilateral symmetrical base are transferred to the re-diagnosed genus Choanocystis and the new genus Pterocystis. The study also presents new information on variability within some species. (ref. ID; 4745)
Type species; Acanthocystis turfacea Carter, 1863 (ref. ID; 4745)

  1. Acanthocystis aculeata Hertwig & Lesser, 1874 (ref. ID; 3541, 3691, 4687, 4710) reported year? (ref. ID; 1335, 1618, 1923) reported author and year? (ref. ID; 4009)
    Syn; Acanthocystis flava Greeff, 1875 (ref. ID; 3691); Acanthocystis serrata Nicholls, 1983 (ref. ID; 4710)
  2. Acanthocystis albida Penard, 1889
    See; Acanthocystis erinaceus Penard, 1889 (ref. ID; 1334, 3691)
  3. Acanthocystis bicornis Durrschmidt, 1987 (ref. ID; 4724 original paper)
  4. Acanthocystis brevicirrhis (Perty, 1852) (ref. ID; 1334, 1923) or (Perty) Wailes, 1921 (ref. ID; 3541)
    Syn; Acanthocystis paludosa West, 1901 (ref. ID; 1334, 3541); Acanthocystis pertyana Archer, 1869 (ref. ID; 1334, 3541)
  5. Acanthocystis chaetophora Leidy, 1879
    See; Acanthocystis turfacea Carter, 1863 (ref. ID; 3541, 3691)
  6. Acanthocystis chetophora (Schrank, 1803) (ref. ID; 1334, 1923)
    Syn; Acanthocystis chetophora Leidy, 1879 (ref. ID; 1334); Acanthocystis pallida Greeff, 1869 (ref. ID; 1334); Acanthocystis turfacea Carter, 1863 (ref. ID; 1334); Acanthocystis viridis Grenacher, 1869 (ref. ID; 1334); Actinophrys viridis Ehrenberg, 1833 (ref. ID; 1334)
  7. Acanthocystis clathrata Durrschmidt, 1985 (ref. ID; 4687 original paper)
  8. Acanthocystis clavata Durrschmidt, 1987 (ref. ID; 4724 original paper, 7658)
  9. Acanthocystis cornuta Durrschmidt, 1987 (ref. ID; 4724 original paper, 4731)
  10. Acanthocystis cordiformis Durrschmidt, 1987 (ref. ID; 4724 original paper)
  11. Acanthocystis cordiformis ssp. parvula Durrschmidt, 1987 (ref. ID; 4724 original paper)
  12. Acanthocystis cuneiformis Durrschmidt, 1985 (ref. ID; 4687 original paper)
  13. Acanthocystis discoidea Durrschmidt, 1985 (ref. ID; 4687 original paper)
  14. Acanthocystis dresscheri Siemensma & Roijackers, 1988 (ref. ID; 4745 original paper)
    See; Pterocystis echinata (ref. ID; 4745)
  15. Acanthocystis echinate Rainer, 1968 (ref. ID; 3541 original paper)
  16. Acanthocystis erinaceoides Petersen & Hansen, 1960 (ref. ID; 3541, 4687) reported year? (ref. ID; 7206) reported author and year? (ref. ID; 4009)
    Syn; Acanthocystis erinaceus Wailes, 1921 (ref. ID; 3541)
  17. Acanthocystis erinaceoides Petersen & Hansen ssp. sculpta Durrschmidt, 1987 (ref. ID; 4725 original paper)
  18. Acanthocystis erinaceus Penard, 1889 (ref. ID; 1334, 3541, 3691)
    See; Choanocystis aculeata (ref. ID; 4745)
    Syn; Acanthocystis albida Penard, 1889 (ref. ID; 1334, 3691)
  19. Acanthocystis erinaceus Wailes, 1921
    See; Acanthocystis erinaceoides Petersen & Hansen, 1960 (ref. ID; 3541)
  20. Acanthocystis flabellata Durrschmidt, 1987 (ref. ID; 4725 original paper)
  21. Acanthocystis flagellata (misspelling flabellata?) ssp. novae-zelandiae Durrschmidt, 1987 (ref. ID; 4725 original paper)
  22. Acanthocystis flava Greeff, 1875 (ref. ID; 3691)
    See; Acanthocystis aculeata Hertwig & Lesser, 1874 (ref. ID; 3691)
  23. Acanthocystis foliacea Durrschmidt, 1985 (ref. ID; 4687 original paper)
  24. Acanthocystis foliacea spp. elongata Durrschmidt, 1987 (ref. ID; 4725 original paper)
  25. Acanthocystis foliacea Durrschmidt, 1985 spp. foliacea (ref. ID; 4725, 4731)
  26. Acanthocystis foliacea spp. truncata Durrschmidt, 1987 (ref. ID; 4725 original paper)
  27. Acanthocystis formosa Durrschmidt, 1985 (ref. ID; 4687 original paper, 4731)
  28. Acanthocystis fortesca Nicholls, 1983 (ref. ID; 7206 original paper)
  29. Acanthocystis granulata Durrschmidt, 1987 (ref. ID; 4724 original paper)
  30. Acanthocystis heterospina Nicholls, 1983 (ref. ID; 7206 original paper)
    See; Acanthocystis penardi (ref. ID; 4724)
  31. Acanthocystis italica Gruber, 1894 (ref. ID; 3541)
  32. Acanthocystis kilianii Durrschmidt, 1987 (ref. ID; 4725 original paper) or 1985 (ref. ID; 4731)
  33. Acanthocystis klepica Huitfeld-Kaas, 1906 (ref. ID; 3541)
  34. Acanthocystis latimarginalis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  35. Acanthocystis lemani Penard, 1891
    See; Raphidocystis lemani Penard, 1891 (ref. ID; 3541, 3691)
  36. Acanthocystis lemani var. plonensis Zacharias, 1894
    See; Raphidocystis lemani Penard, 1891 (ref. ID; 3541, 3691)
  37. Acanthocystis longiseta Penard, 1901 (ref. ID; 3541, 3691)
  38. Acanthocystis ludibunda Penard, 1901 (ref. ID; 3691)
    See; Rabdiophrys ludibunda (Penard, 1901) Rainer, 1968 (ref. ID; 3541)
  39. Acanthocystis mimetica Penard, 1904 (ref. ID; 3541, 3691 original paper)
  40. Acanthocystis myriospina Penard, 1890 (ref. ID; 3541, 3691, 4687) reported year? (ref. ID; 1334, 1923)
    Syn; Acanthocystis trifurca Nicholls, 1983 (ref. ID; 4710)
  41. Acanthocystis nichollsi Siemensma & Roijackers, 1988 (ref. ID; 4745 original paper)
  42. Acanthocystis ovata Durrschmidt, 1987 (ref. ID; 4725 original paper)
  43. Acanthocystis paliformis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  44. Acanthocystis pallida Greeff, 1869
    See; Acanthocystis turfacea Carter, 1863 (ref. ID; 3541, 3691)
  45. Acanthocystis pantopoda Penard, 1904 (ref. ID; 3541, 3691 original paper, 4724)
  46. Acanthocystis pantopodeoides Nicholls, 1983 (ref. ID; 4745, 7206 original paper)
    See; Pterocystis fortesca (ref. ID; 4745)
  47. Acanthocystis pectinata Penard, 1889 (ref. ID; 3541, 3691, 4724) reported author and year? (ref. ID; 4009), emend. Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper), emend. Nicholls, 1983 (ref. ID; 7206 redescribed paper)
  48. Acanthocystis pectinata Penard, 1898 (1889 misspelling?) ssp. ceylanica Durrschmidt, 1987 (ref. ID; 4724 original paper)
  49. Acanthocystis pectinata Penard, 1889 ssp. malayensis Durrschmidt, 1987 (ref. ID; 4724 original paper)
  50. Acanthocystis pelagica Ostenfeld, 1904 (ref. ID; 3541, 4687)
  51. Acanthocystis penardi Wailes, 1925 (ref. ID; 3541, 4724) reported author and year? (ref. ID; 4009)
    Syn; Acanthocystis heterospina Nicholls, 1983 (ref. ID; 4724); Acanthocystis spinifera Penard, 1904 nec Greeff, 1869 (ref. ID; 3541, 4724)
  52. Acanthocystis penardi Wailes, 1925 ssp. pusilla Durrschmidt, 1987 (ref. ID; 4724 original paper)
  53. Acanthocystis perpusilla Petersen & Hansen, 1960 (ref. ID; 3541, 4687)
  54. Acanthocystis pertusa Durrschmidt, 1987 (ref. ID; 4724 original paper)
  55. Acanthocystis pertyana Archer, 1869 (ref. ID; 3691) or (Archer) Penard, 1904 (ref. ID; 3541)
  56. Acanthocystis pinnata Nicholls, 1983 (ref. ID; 4725)
  57. Acanthocystis pinnata Nicholls, 1983 (ref. ID; 4725, 7206 original paper)
  58. Acanthocystis plumosa Durrschmidt, 1987 (ref. ID; 4725 original paper)
  59. Acanthocystis polymorpha Durrschmidt, 1985 (ref. ID; 4687 original paper)
  60. Acanthocystis pteromorphos Durrschmidt, 1987 (ref. ID; 4725 original paper)
  61. Acanthocystis pulchra Durrschmidt, 1985 (ref. ID; 4687 original paper, 4725)
  62. Acanthocystis pyriformis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  63. Acanthocystis quadrifurca Nicholls, 1983 (ref. ID; 7206 original paper)
  64. Acanthocystis rasilis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  65. Acanthocystis rhytidos Durrschmidt, 1987 (ref. ID; 4724 original paper)
  66. Acanthocystis rotundata Nicholls, 1983 (ref. ID; 4724, 7206 original paper)
  67. Acanthocystis rotundata Nicholls, 1983 ssp. rotoairense Durrschmidt, 1987 (ref. ID; 4724 original paper)
  68. Acanthocystis rubella Penard, 1904 (ref. ID; 3541, 3691 original paper) reported year? (ref. ID; 2240)
    See; Rabdiophrys rubella (Penard, 1904) (ref. ID; 3541)
  69. Acanthocystis serrata Nicholls, 1983 (ref. ID; 7206 original paper)
    See; Acanthocystis aculeata (ref. ID; 4710), Choanocystis aculeata (ref. ID; 4745)
  70. Acanthocystis setifera Minkevich, 1898 (ref. ID; 3541)
  71. Acanthocystis simplex Schaudinn, 1898 (ref. ID; 3541) reported year? (ref. ID; 3691)
    See; Raphidocystis simplex (Schaudinn, 1898) (ref. ID; 3541, 3691)
  72. Acanthocystis spinifera Greeff, 1869 (ref. ID; 3541) reported year? (ref. ID; 1334), Greeff, 1869 emend. Penard (ref. ID; 3691) or Greeff, 1869 emend. Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper)
  73. Acanthocystis spinifera Penard, 1904
    See; Acanthocystis penardi Wailes, 1925 (ref. ID; 3541)
  74. Acanthocystis striata Nicholls, 1983 (ref. ID; 4710, 4725)
  75. Acanthocystis takahashii Durrschmidt, 1987 (ref. ID; 4724 original paper)
  76. Acanthocystis trifurca Nicholls, 1983 (ref. ID; 7206 original paper)
    See; Acanthocystis myriospina (ref. ID; 4710)
  77. Acanthocystis tropica Durrschmidt, 1987 (ref. ID; 4725 original paper)
  78. Acanthocystis tropica ssp. paucistriata Durrschmidt, 1987 (ref. ID; 4725 original paper)
  79. Acanthocystis tubata Durrschmidt, 1987 (ref. ID; 4724 original paper)
  80. Acanthocystis turfacea Carter, 1863 (ref. ID; 3541, 3691, 4687, 4710) reported year? (ref. ID; 7206) reported author and year? (ref. ID; 4009)
    Syn; Acanthocystis chaetophora Leidy, 1879 (ref. ID; 3541) reported year? (ref. ID; 3691); Acanthocystis pallida Greeff, 1869 (ref. ID; 3541) reported year? (ref. ID; 3691); Acanthocystis viridis Grenacher, 1869 (ref. ID; 3541) reported year? (ref. ID; 3691); Actinophrys viridis Ehrenberg (ref. ID; 3691)
  81. Acanthocystis turfacea var. simplex Wailes, 1925 (ref. ID; 3541)
  82. Acanthocystis umbraculiformis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  83. Acanthocystis valdiviense Durrschmidt, 1987 (ref. ID; 4724 original paper)
  84. Acanthocystis veliformis Durrschmidt, 1987 (ref. ID; 4725 original paper)
  85. Acanthocystis viridis Grenacher, 1869
    See; Acanthocystis turfacea Carter, 1863 (ref. ID; 3541, 3691)
  86. Acanthocystis wiasemskii Ostroumoff, 1917 (ref. ID; 3541, 7658 redescribed paper)

Acanthocystis aculeata Hertwig & Lesser, 1874 (ref. ID; 3541, 3691, 4687, 4710) reported year? (ref. ID; 1335, 1618, 1923) reported author and year? (ref. ID; 4009)

Synonym

Acanthocystis flava Greeff, 1875 (ref. ID; 3691); Acanthocystis serrata Nicholls, 1983 (ref. ID; 4710)

Descriptions

Tangential scales stout and pointed; spines curved and nail-headed; cytoplasm greyish a single contractile vacuole; spines about one-third the body diameter; in fresh water. (ref. ID; 1618)
This species possesses radial spines nail-headed in form, with the base enlarged. (ref. ID; 1923)
Periplast 21-67 um in diameter (in literature), 40-50 um (measurement based on whole mounts). Plate scales heavily silicificated, 4.9-11x2.8 um, arranged in several compact layers. In dorsal projection the plate scales are normally dumb-bell-like, caused by deep median construction. But many aberrant forms exist, probably released unfinished or apparently originating from inner scale layers, as they have not been observed on the periphery of the periplasts by SEM. The spine scales are numerous 6-15 um long, provided with a cordiate, slightly convexly depressed base-plate. The shaft is eccentrically attached close to the indentation of the base-plate. Short irregularly shaped protrusions are present, mainly along the proximal part of the shaft. Towards its distal end the shaft narrows slightly, terminating abruptly with 2 or 3 in teeth. (ref. ID; 4687)
Two forms of A. aculeata were observed, one with short irregularly shaped protrusions on the shaft of the spine scales, and one without. Cells of the former were 19.7-23.5 um in diameter, with spine scales 6.6-13.1 um long having a base plate 1.7-2.7 um in diameter and lateral nodules and papillae along the proximal one third of the shaft, and with dumbbell shaped plate-scales 4.9-5.7 by 2.6-3.5 um with a median construction 1.2-2.6 um wide. Cells of the latter were around 15 um diameter, with spine scales 3.0-8.0 um long, having a base plate 1.43-1.70 um in diameter and a smooth shaft, and with dumbbell shaped plate-scales 4.0-5.0x1.7-2.5 um with a median constriction 1.1-1.5 um wide. The apex of the shaft of the spine scales of both forms was blunt, with several small teeth. (ref. ID; 4710)

Remarks

Hertwig and Lesser described A. aculeata from small ponds in the vicinity of Bonn/F.R.G. A reproduction of the original drawing is given. It is one of the most frequently recorded Acanthocystis species, easily recognizable with the light microscope. Its mode of action and its internal structure have been intensely studied not only by light microscopy (e.g. Stern 1924; Schaudinn 1896) but also by thin sectioning (Bardele 1977). Some taxonomic uncertainty pertains to the marine A. pelagica Ostenfeld, 1904, which is apparently identical with A. aculeata, since there are dump-bell-like plate scales and similar spine scales. There is as yet no information as to whether A. aculeata even tolerates salt water conditions, making further investigations necessary before both species are considered synonymous. (ref. ID; 4687)

Measurements

Diameter 35-40 um. (ref. ID; 1618)

Acanthocystis bicornis Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 15-25 um in diameter (measurement based on whole mount), with 3 types of scales. Sine scales consisting of base-plate, shaft and furcate apex. Shaft narrow, cylindrical, 0.12 um thick. Base-plate, 0.6-0.8 um in diameter, circular, with a slightly upturned peripheral edge. Large spine scales, 4-5 um long, with 1 tooth on the inner edge of each branch of the apical furca (furca ca. 0.7 um long). Distal ends canted. Small spine scales, 2.0-3.2 um long, a broader fork in the apex, usually with one or two teeth of varying length present on the inner edge of each branch. Tip of the branches biforked to a varying length. Plate scales, 2.7x1.6 um, elliptical, sometimes slightly curved, patternless, except for the axial thickening. (ref. ID; 4724)

Remarks

A. bicornis is easily distinguished from all other species of Acanthocystis by the distinctly bifurcate tips of the small spine scales in addition to teeth on each apical branch. Nicholls (1983) reports Canadian specimens of A. turfacea with "tiny teeth on the bifurcate apices of the long spines". However, the forks of the small spine scales are smooth and pointed. A. cornuta also has teeth along the inner edge of the branches of the apical furca by differs in that there are always three or more teeth present, and in that it has only one spine scale type. A survey of all scales hitherto examined shows that there are only minor variations in the spine scale structure among specimens from different sources. A. bicornis has been found in a small swamp on the Puyehue Pass Road, southern Chile (July 1981) and in a small shallow pond near Batticaloa, E. Sri Lanka. (ref. ID; 4724)

Etymology

From the Latin bicornis, double-horned. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected 15 July 1982 from Lake Ngahewa, 3 km NNE of Waiotapu, North Island, New Zealand and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.9; 1984.12.17.10). (ref. ID; 4724)

Acanthocystis brevicirrhis (Perty, 1852) (ref. ID; 1334, 1923) or (Perty) Wailes, 1921 (ref. ID; 3541)

Synonym

Acanthocystis paludosa West, 1901 (ref. ID; 1334, 3541); Acanthocystis pertyana Archer, 1869 (ref. ID; 1334, 3541)

Descriptions

This species has short, straight or slightly curved spines. (ref. ID; 1923)

Acanthocystis chetophora (Schrank, 1803) (ref. ID; 1334, 1923)

Synonym

Acanthocystis chetophora Leidy, 1879 (ref. ID; 1334); Acanthocystis pallida Greeff, 1869 (ref. ID; 1334); Acanthocystis turfacea Carter, 1863 (ref. ID; 1334); Acanthocystis viridis Grenacher, 1869 (ref. ID; 1334); Actinophrys viridis Ehrenberg, 1833 (ref. ID; 1334)

Descriptions

The skeleton plates are oval, arranged tangentially and slightly imbricated. The spinous rays are of 2 kinds, the numerous long ones acutely forked, the less numerous short ones widely forked at the distal extremities. Nucleus large, eccentric; no contractile vacuole. Endoplasm green in color, enclosing zoochlorellae. Habitat lakes, ponds, and moorland pools. (ref. ID; 1923)

Measurements

Diameter of the body 35-60 um, rarely up to 100 um. (ref. ID; 1923)

Acanthocystis clathrata Durrschmidt, 1985 (ref. ID; 4687 original paper)

Diagnosis

Periplast 20-30 um in diameter (measurement based on whole mount); details of the protoplast unknown. The scales are characteristically of 2 types, namely ellipsoidal, rounded or oval plate scales, and numerous 5-10 um long spine scales. The plate scales, 2.5-3.2x1.5-2.2 um, have a pattern of spoke-like struts occupying the major part of the scale. These struts radiate between the rather narrow and smooth peripheral margin and the central patternless area. The plate scales become slightly thicker towards their centre, where they have the typical central ridge. The spine scales possess the customary tubular, slightly tapering shaft, 0.1-0.2 um in diameter, a plate-like basis, and distally four small teeth. (ref. ID; 4687)

Remarks

Wheel-like plate scales have not been previously reported from members of the genus Acanthocystis. Nevertheless, these scales also have the characteristic central ridge and shape of typical Acanthocystis plate scales and might represent a unique evolutionary line. Moreover, the spine scales are of the same appearance as those in Acanthocystis myriospina, which differ only in having distal ends with three rather than four teeth. Despite the basis similarity between A. myriospina and A. clathrata, they are different from each other at a specific rather than subspecific level due to the distinguishing feature of the plate scales. (ref. ID; 4687)

Etymology

The epithet "clathrata" refers to the lattice-like appearance of the plate scales. (ref. ID; 4687)

Type locality

Swamp, 10 km south of Puerto Montt on the road to Pargua (loc. 6). Collected on July 17, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:3). (ref. ID; 4687)

Acanthocystis clavata Durrschmidt, 1987 (ref. ID; 4724 original paper, 7658)

Diagnosis

Periplast, 25-30 um, in diameter (measurement based on whole mount); details of protoplast unknown. There are two types of scales: plate scales and nail-like spine scales. Plate scales, 1.3x0.77 um, are elliptical and slightly curved or ovoid. They are thin and patternless, except for a poorly developed central thickening. Spine scales, up to 10 um long, straight or moderately curved, with a circular base-plate, 0.4 um in diameter. Shaft presumably solid, slightly narrowing to a thin, but blunt apex. (ref. ID; 4724)

Remarks

There is a certain similarity between A. clavata and A. spinifera Greeff (1869) as regards size and shape of cells and spine scales. Recent investigation have revealed (Nicholls 1983; Durrschmidt 1985) that there are several species of almost identical light microscopic appearance, which is why an identification of A. clavata with A. spinifera appears rather arbitrary. With an electron microscope A. clavata can be easily recognized by the shape of the spine scales. It is distinguished from all other so far known a Acanthocystis species belonging to Group A by its tapering shaft and closed apex. (ref. ID; 4724)

Etymology

From the Latin clavata, nail-shaped. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected on 15 September 1975 from Banado Cruces (Station 8, see Durrschmidt 1980), Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.2). (ref. ID; 4724)

Acanthocystis cornuta Durrschmidt, 1987 (ref. ID; 4724 original paper, 4731)

Diagnosis

Periplasts, ca. 15-20 um in diameter (measurement based on whole mount), with two types of scales. Details of protoplast unknown. Spine scales, 3.2 to 4.4 um long, consisting of base-plate, shaft and forked apex. Shaft, 0.1 um thick, cylindrical and hollow. Base-plate circular, 0.5 um in diameter. Apex furcated with two diverging and tapering branches, ca. 1 um long. Inner edge of each branch with 2-4 pointed teeth, outer edge smooth. Plate scales elliptical, 2.3-3.0x1.5-1.9 um, with a small peripheral rim. Ornamentation consists of an axial thickening oriented longitudinally and faintly developed radial slits. (ref. ID; 4724)

Descriptions

The single spine scale observed was 7.5 um long with a base plate diameter of 0.65 um and apical branches 0.7 um long. The 4-5 teeth on the inner edges of the apical branches were well formed and prominent. The presence of such teeth is presently diagnostic of A. cornuta (Durrschmidt, 1987), but the spine scale observed was much longer than those recorded for A. cornuta (7.5 um against 3.2-4.4 um) and the teeth appeared to be more prominent. In the absence of any periplast or plate scale observations the spine scale is simply recorded here as being allied to those of A. cornuta. (ref. ID; 4731)

Remarks

A. cornuta most closely resembles A. radiosa Roskin (1929) and A. pectinata Penard, 1889 sensu Penard (1904), the only previously known Acanthocystis species with a single type of forked spine scales, and A. bicornis (this paper), from which it differs (1) in having only one type of spine scale, (2) in having more than 2 teeth along the inner edge of the apical furca, and (3) in the faint slit-pattern of the plate scales. (ref. ID; 4724)

Etymology

From the Latin cornuta, horn-shaped. (ref. ID; 4724)

Type slide

The specimens found in a water sample collected 3 July 1981 from a paludal forest (hualve) near Lake Lanalhue, Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.8). (ref. ID; 4724)

Acanthocystis cordiformis Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 40-50 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales (11), 16-20 um long, narrow, consisting of shaft and base-plate. Shaft, 0.15-0.25 um in diameter, cylindrical, solid (?), tapering slightly to a blunt apex with 4-6 tiny marginal teeth. Proximal part of the shaft sometimes with minute siliceous nodules. Base of the spine seated eccentrically on a thin, heart-shaped base-plate, 0.5 um in diameter. Plate scales elliptical, 1.5-2.2x1.0-1.5 um, patternless, except for an axial thickening. (ref. ID; 4724)

Remarks

Among the Acanthocystis species so far known, A. cordiformis, closely resembles A. pantopoda Penard, A. perpusilla Petersen and Hansen (1960) and A. rotundata Nicholls (1983) in that the spine scales have heart-shaped bases, usually smooth shafts and patternless plate scales. Whether the shafts are solid or hollow is not clearly visible and has still to be established by thin sectioning. Distinguishing features are the length and breadth of the spine scales, the degree of tapering, the elaboration of the base-plate and the appearance of the plate scales. From TEM micrographs it is evident that this species group is taxonomically one of the most difficult ones of Acanthocystis despite the assistance given by electron microscopy. This applies in particular to the lack of other fine structural characteristics. Clonal tests are therefore very necessary to clear up the current, rather confusing taxonomic situation. (ref. ID; 4724)

Etymology

From the Latin cordiformis, heart-shaped. (ref. ID; 4724)

Type slide

Type specimen collected 7 March 1983 in Tissa Lake, S. Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.12). (ref. ID; 4724)

Acanthocystis cordiformis ssp. parvula Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Differs from the type in that the spine scales are distinctly smaller. Periplast, 25-32 um in diameter (measurement based on whole mount); spine scales, 6-8 um long; shaft, 0.16 um thick; base-plate 1.1 um in diameter; plate scales, 2.3-3.2x1.6-1.8 um. (ref. ID; 4724)

Remarks

Due to the similarity of the spine scales with those of A. cordiformis, these specimens are only described on subspecific level. A. cordiformis ssp. parvula is also closely related to A. perpusilla Petersen and Hansen (1960) in the construction of the spine scales. However, the spine scales of A. perpusilla are only half the size of those of A. cordiformis ssp. parvula are often remarkably curved. No typical A. perpusilla cells have been found together with A. cordiformis ssp. parvula. This and the uniformity of the scale size seems to indicate that these specimens belong to a separate taxon. It is classified as a member of A. cordiformis on the slightly closer resemblance to the former. Similar specimens are depicted by Nicholls (1983) from Canada but tentatively assigned to A. myriospina Penard sensu Nicholls. From EM micrograph no. 8 in Nicholls (1983) it is evident, that the shafts are eccentrically seated on the presumably heart-shaped base-plates, which is characteristic for spine scales of Group B. A. cordiformis ssp. parvula was found together with specimens ascribed to A. cordiformis from which it could always be easily distinguished by its shorter and tapering spine scales and by the partly hollow shafts. No transitional specimens have been observed. (ref. ID; 4724)

Etymology

From the Latin parvulus, small. (ref. ID; 4724)

Type slide

Type specimen collected 6 March 1983 in a small pond near Batticaloa, E. Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.13). (ref. ID; 4724)

Acanthocystis cuneiformis Durrschmidt, 1985 (ref. ID; 4687 original paper)

Diagnosis

Periplasts 40-60 um in diameter (measurement based on whole mount). Scales of 2 types. Details of protoplast unknown. Plate scales, 2.2-3.5x1.1-2.1 um, in dorsal projection more or less elliptical, are thin and weakly silicified. There is a narrow slightly thickened margin and a rudimentary central ridge. Scanning micrographs indicate a distinctly depressed middle part followed by a more or less upturned submarginal part. The spine scales are conspicuously long in relation to the specific cell diameter. The shaft, 13-15 um long, ca. 0.22 um in diameter, is thin and tubular, terminating distally in a crenulate margin and proximally with a "shovel-like" structure. There, the shaft carries 2 short lateral extensions (= the lateral wings) in an almost V-form arrangement relative to the main axes, and additionally a further extension (= the basal wing), which spreads between the ventral edges of the lateral wings. The anterior part of the basal wing is gently curved carrying several ribs, which appear in TEM as dark lines. Sometimes a few cross-ribs are also present on the backwardly bent flanges of the lateral wings. The typical shovel-like appearance, hence the specific epithet, is caused by the tapering shaft end, which is curved conspicuously outwards. (ref. ID; 4687)

Remarks

There are several unusual features about this species: the exceptionally long and thin spine scales, their shovel-like bases not previously observed in an Acanthocystis species, and the non-flat plate scales. As the spine scales remain firmly attached to the plate scale layer, even during fixation, it seems possible that their bases cling to the strongly concave middle part of the plate scales. This was, however, not confirmed when seen in SEM. Thin sectioning would add more information to the relative position of these two scale types. Concerning the scale structure, A. cuneiformis has some features in common with A. erinaceoides: e.g. the laterally winged shaft bases, but differs essentially in the possession of an additional basal wing, non-tapering distal shaft ends, and in the deeply concave plate scales. (ref. ID; 4687)

Type locality

Banado Rio Cruces (loc. 2). Collected on July 25, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:4). (ref. ID; 4687)

Acanthocystis discoidea Durrschmidt, 1985 (ref. ID; 4687 original paper)

Diagnosis

Periplast small, ca. 10-15 um in diameter (measurement based on whole mount), with 2 types of scales. Protoplast unknown. Plate scales small, 1.1x0.6-0.75 um, ovoid and thin. The central ridge is slightly shifted to the smaller pole of the scale. There is a gently depressed middle part and slightly inflexed margins. The spine scales, 3.4-4.1 um in diameter, are almost circular or roundly oval. They are divided into a broad patternless marginal band and a ribbed central area. The "shaft" is indicated only by the dark central line, from which ribs radiate to the inner margin of the smooth band. A slight depression at one end of the "shaft" may indicate its basal part. (ref. ID; 4687)

Remarks

This very interesting small Acanthocystis species is conspicuous by virtue of its smooth, rounded, discus-like "spine scales", not previously observed in Acanthocystis. All the typical features of the spine scales, such as shaft, wings, baseplates etc., are modified to such a degree that even the denomination of the apparently homologous structures remains somewhat vague in A. discoidea. There is nothing known about the attachment of the "spine scales" and their relative position to the subtending plate scales in A. discoidea. (ref. ID; 4687)

Etymology

The epithet "discoidea" refers to the discus-shaped spine scales. (ref. ID; 4687)

Type locality

Small pond, 14.8 km north of Valdivia on the right hand side of the northbound Pan American Highway, loc. 3. Collected on July 5, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:8). (ref. ID; 4687)

Acanthocystis dresscheri Siemensma & Roijackers, 1988 (ref. ID; 4745 original paper)

See

Pterocystis echinata (ref. ID; 4745)

Diagnosis

Cell diameter 20 um. Spine-scales 7.3-10.3 um long, with a straight, cylindrical, hollow shaft, 0.5-0.7 um in diameter, centrally set on a circular basal plate. The apex of the shaft is slightly expanded, 0.6-0.8 um in diameter, with 5-8 marginal sharply pointed teeth, each ca. 0.13 um long. The basal plate is 1.4-2.2 um in diameter, flat, with an upwardly bent rim, ca. 0.14 um thick. The plate-scales are 4.7-5.5x2.3-3.0 um, having concave sides with the median constriction 1.5-2.4 um wide; the upper surface is ornamented with a distinct pattern of numerous small granules, more or less irregularly distributed, sometimes arranged in concentric rows; central area smooth with a slight indication of a longitudinal thickening. The lower surface is smooth with a protrusive axial rod-shaped thickening, distinctly separated from the scale surface and only at both ends merging into the scale. The protrusion is 0.43 um thick and ca. 1.3 um long. The protrusion on the lower side of the plate-scales is the most remarkable feature of this species. A. dresscheri shows some similarity with A. longiseta Penard, 1901, diagnosed as having rod-like or irregular plate-scales (Penard 1904). It is not unlikely that Penard mistook the rod-like protrusion, present in plate-scales of A. dresscheri, for the whole plate-scale, as indicated by Siemensma (1981: plate 41 E, F). The main distinction between these two species is the presence of spine-scales of the same length (A. longiseta) and of short and long spine-scales (A. dresscheri). The diagnosis of A. longiseta was changed by Penard (1905), by describing the plate-scales as elliptical and without any longitudinal thickening, which indicates the problems of distinguishing among species by light microscopy. (ref. ID; 4745)

Comments

A. dresscheri is closely related to A. penardi, but this species, SEM-studied by Siemensma (1981), Nicholls (1983, as described as A. heterospina) and Durrschmidt (1987), has smooth, elliptical or slightly constricted plate-scales, without any longitudinal rod-shaped protrusion. No other species with in the genus Acanthocystis, as re-diagnosed in this paper, is known to have such a protrusive longitudinal thickening. (ref. ID; 4745)

Etymology

The specific name is given in honour of Mr. Th.G.N. Dresscher. (ref. ID; 4745)

Type locality

A. dresscheri has been recognised in samples taken from a moorland pool (pH 5.5) near Nunspeet, the Netherlands. The samples are from the collection of the late Mr. Th.G.N. Dresscher, who identified the specimens as Acanthocystis penardi, not knowing the characteristic ultrastructure. (ref. ID; 4745)

Acanthocystis erinaceoides Petersen & Hansen, 1960 (ref. ID; 3541, 4687) reported year? (ref. ID; 7206) reported author and year? (ref. ID; 4009)

Synonym

Acanthocystis erinaceus Wailes, 1921 (ref. ID; 3541)

Remarks

The structure of the scales is in agreement with the type description of Petersen and Hansen (1960). However, the plate scales, reported to possess a small central furrow, have to be interpreted as provided with an apparently hollow central swelling. Scanning micrographs show that in dorsal projection the plate scales reveal a distinct convex projection and not a furrow. In TEM this are appears less dense than the surrounding part, which is also visible in Petersen and Hansen (1960, micrograph no. 1), thus the swelling is assumed to be hollow. However, this has to be proved by thin-sectioning. (ref. ID; 4687)
Acanthocystis erinaceoides was previously known only from Denmark (Petersen & Hansen 1960). The organisms from Crystal, Calabogie, and Lloyd lakes agree well with the description of the type except that a considerably wider range in cell size (15-40 um, excluding spines) and axopodium length (up to 80 um) was observed. The Danish type specimen was 23.5 um in diameter with axopodia up to 56 um long. The shapes of the spine-scales and plate-scales show only minor variation among specimens from the three Ontario lakes are essentially identical in structure to the Danish material. (ref. ID; 7206)

Acanthocystis erinaceoides Petersen & Hansen ssp. sculpta Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. erinaceoides ssp. erinaceoides in that the plate scales possess numerous cross-slits (0.4 um long), proceeding from the central swelling and ending a certain distance from the peripheral rim. The spine scales reveal longitudinally extended lateral wings, which often reach the distal third of the shaft. Periplast 20-35 um, spine scales 6-12 um long, plate scales 4.6 to 5.0 x 2.2-2.8 um. (ref. ID; 4725)

Remarks

See A. erinaceoides ssp. undulata. (ref. ID; 4725)

Etymology

From the Latin sculpta, carved out. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 7 March 1983 from Tissa Lake, southern Sri Lanka, and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.1). (ref. ID; 4725)

Acanthocystis erinaceoides Petersen & Hansen ssp. undulata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. erianceoides ssp. erinaceoides in the conspicuous undulate margins of the lateral wings, which sometimes appear even frayed. The plate scales differ in having numerous narrow cross-slits and irregularly scattered dots. Periplasts ca. 25 um in diameter, spine scales 4.3-5.0 um long, plate scales 2.2-2.8x1.1 um. (ref. ID; 4725)

Remarks

The close relationship of these specimens to A. erinaceoides Petersen and Hansen (1960) is evident not only in the presence of the characteristic central swelling of the plate scales, but also by the similar form of the spine scales. Distinctive features, however, are the slitted plate scales and in the case of ssp. undulata the markedly undulate margins of the lateral wings of the spine scales. Though these differences appear relatively minor, no intermediate forms have been observed and both characteristics were found stable even in individuals from widely separated areas like Chile and Sri Lanka. Moreover, a recent study of the range of infraspecific variation using clonal cultures of A. erinaceoides ssp. erinaceoides (Patterson and Durrschmidt, in prep.) has proved that the morphology of the scales is remarkably uniform, permitting clear distinction between all so far known subspecies. In regard to the plate scales, it is notable that the slit-pattern in ssp. sculpta is clearly detectable by SEM, whereas it is below the resolution of the SEM used in ssp. undulata. The specimen shows spine scales, which are somewhat reminiscent of A. pinnata Nicholls (1983) in that they have broad lateral wings. (ref. ID; 4725)

Etymology

From the Latin undulatus, undulate. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 7 March 1983 from Tissa Lake, southern Sri Lanka, and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.2). (ref. ID; 4725)

Acanthocystis flabellata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast, 10-15 um in diameter (measurement based on whole mount) with two types of scales; details of protoplast unknown. The spine scales are radial symmetrical, 3.6 um in diameter and 2.7 um long, with regularly spaced ribs which are composed of 3-4 smaller ribs. These radiate from the upper end of the stalk to the outer margin. A shaft is not developed. The stalk is short (0.5 um), smooth, cylindrical and closed on its basal end, however, this delicate layer is often torn. The plate scales, 1.2-2.0x0.7-1.1 um, are ovoid or elliptical with an axial thickening shaft slightly towards the smaller pole of the scale. Peripheral the scales are surrounded with a narrow inflexed rim. (ref. ID; 4725)

Remarks

This very interesting small Acanthocystis species is conspicuous by virtue of this radially symmetrical spine scales. All the typical features such as shaft, wings, base-plates etc. are modified to such a degree that they are no longer distinguishable. Only the short stumpy stalk and the rib pattern are somewhat reminiscent of the spine scales of A. pulchra. It is suggested that the spine scales of A. flabellata have been derived as modified A. pulchra spine scales by reproduction of the stalk and the regular elaboration of the "winged area". There is no indication of what has become of the shaft. However, the regularly radiating rib pattern can only be obtained when (compare with A. formosa) the shaft is shortened to make way for a complete radial symmetrical arrangement. (ref. ID; 4725)

Etymology

From the Latin flabellatus, fan-shaped. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 20 July 1981 from a swamp on Puyehue pass road in Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.15). (ref. ID; 4725)

Acanthocystis flagellata (misspelling flabellata?) ssp. novae-zelandiae Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. flabellata ssp. flabellata in that the spine scales are bowl-shaped without a smooth stalk-like basal protrusion. In all other respects they are identical. Periplast 10-15 um, spine scales 3.8 um in diameter and 3 um long, plate scales 1.2-2.0x0.7-1.1 um. (ref. ID; 4725)

Remarks

On first sight the spine scales of the New Zealand specimens appear almost identical with those of ssp. flabellata. However, the stalk is completely reduced, so that the basal part appears blunt and rounded. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 15 July 1982 from Lake Ngahewa, North Island, New Zealand and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.16). (ref. ID; 4725)

Acanthocystis foliacea Durrschmidt, 1985 (ref. ID; 4687 original paper)

Diagnosis

Periplast small, ca. 10-20 um in diameter (measurement based on whole mount) with 2 types of scales. Details of protoplast unknown. Plate scales, 2.5-3.1x1.8-2.0 um are ellipsoidal, sometimes slightly curved or with a median construction. The scales are thin and narrow-rimmed. The central ridge is only noticeable as a somewhat darker central line. Spine scales, 2.2-6.9 um long, are almost leaf-like (hence the specific epithet). The shaft is reduced to a narrow ridge, in TEM appearing as a dark line between the two conspicuously broad lateral wings. These are developed along the whole shaft and taper distally into a small tip, obviously the terminal part of the shaft. They broaden gently towards the proximal end but, at a short distance from these, they narrow abruptly from a short compact stalk. The more or less horizontal extension opposite the shaft may be conceived as a modified basal wing, especially as some scales reveal rudimentary demarcations between the lateral wings and the "basal wing". The wings are patternless with smooth, narrow-rimmed margins. Periplasts with exceptionally small, somewhat reduced spine scales, which are even smaller than their plate scales, were observed, too. They are further distinguished by their hollow, relatively long stalks in relation to the length of the spine scale itself, the hardly recognizable shaft, and the short wings with a bluntly pointed distal end. (ref. ID; 4687)

Remarks

Some of the more perplexing components of the periplast of this small Acanthocystis species are the morphology of the spine scales, and the fact that they remain closely attached even after fixation and drying. In particular, the spine scales are quite unlike an Acanthocystis species, although the leaf-like appearance may be attributed to modified lateral and basal wings in connection with a great reduction of the shaft. Also, the short stalk can be interpreted as being formed by shaft, lateral wings and basal wing. Our uncertainty pertains to the differences in shape and size of the spine scales, which could represent genuine differences between individual specimens, which may or may not be taxonomically significant. The reason for including them all within one diagnosis is that in spite of the differences in size they share the characteristic leaf-like shape distinguishing them from other members in Acanthocystis. (ref. ID; 4687)

Type locality

Swamp on the shallow northern shore of Lake Calafquen, loc. 1. collected on July 21, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:5). (ref. ID; 4687)

Acanthocystis foliacea spp. elongata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. foliacea ssp. foliacea in having more narrow, elongated spine scales, a shaft which extends past the distal end of the lateral wings, and a truncated apex. Periplast 20-30 um in diameter, spine scales 5.5-6.3 um long, plate scales 2.5-3.1x1.8-2 um. (ref. ID; 4725)

Remarks

This subspecies is particularly interesting in that the shaft end extends past the lateral wings, although not far, and, therefore fits closely into the shaft-reducing-line from A. erinaceoides to A. rasilis. The spine scale pictured in Fig. 51 in Durrschmidt (1985) belongs also to ssp. elongata. Single spine scales were illustrated by Takahashi (1959, Pl.IX, Fig.72) from Japan, as microplankton sp. no. 15 from Arasawa dam. (ref. ID; 4725)

Etymology

From the Latin elongatus, elongate. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 7 March 1983 from Tissa Lake, Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.8). (ref. ID; 4725)

Acanthocystis foliacea Durrschmidt, 1985 spp. foliacea (ref. ID; 4725, 4731)

Descriptions

Only one spine scale of A. foliacea was observed, 3.4 um long by 2.3 um broad. The spine scales of A. foliacea are variable in shape but to date only two subspecific groups have been delineated, the foliacea group and the elongata group. Because of its width relative to length and the fact that the shaft of the spine scale does not extend past the lateral wings, the Australian specimen belongs to the foliacea group. (ref. ID; 4731)

Acanthocystis foliacea spp. truncata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. foliacea ssp. foliacea in having smaller, truncated, spine scales. Wings are always present along the total length of the shaft. Periplasts 6-10 um, spine scales 1.9-2.7 um long, 1.8-2.2 um wide, plate scales 2.3-3.0x1.8-2 um. (ref. ID; 4725)

Remarks

The cell and spine scale dimensions of the new subspecies are remarkably small. However, the plate scales are to be found of the same size as in the other two subspecies. (ref. ID; 4725)

Etymology

From the Latin truncatus, deformed. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 7 March 1983 from Tissa Lake, Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.9). (ref. ID; 4725)

Acanthocystis formosa Durrschmidt, 1985 (ref. ID; 4687 original paper, 4731)

Diagnosis

Periplast small, ca. 10-15 um in diameter (measurement based on whole mount), with 2 types of scales. Details of protoplast unknown. Plate scales, 1.2-1.5x0.9-1.0 um, ellipsoidal or slightly asymmetrically shaped. They are thin with a central depression, upturned submarginal parts and slightly inflexed margins. The spine scales are almost circular or oval, 3.1-3.5 um in diameter, with regularly spaced delicate ribs of regular width, which radiate from the shaft to the outer margin. The shaft is rudimentary, present only as a somewhat broader dark line. The area round the "shaft base" is concavely depressed. The lateral wings and the basal wing join on the nearly circular form of the spines scale. (ref. ID; 4687)
The spine scales observed were almost circular, around 3.0 um in diameter, and very similar to those described from Chile. (ref. ID; 4731)

Remarks

The reason for including these specimens within the genus Acanthocystis is that, in spite of the very different spine scales, they share the characteristic plate scales. Scale distribution in the periplast is complicated by the fact, that the method of attachment of the spine scales could not be directly observed in whole mounts. It is assumed that they cling with their slightly depressed middle parts to the plate scales, while laterally overlapping other spine scales. The plate scales seem to be clustered in several layers under the spine scales. But thin-sectioning is necessary to reveal their relative positions in the periplast. (ref. ID; 4687)

Etymology

The epithet "formosa" refers to the delicate spine scales. (ref. ID; 4687)

Type locality

Pools in a Sphagnum magellanicum bog, 12 km north of Castro (loc. 8). Collected on July 13, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:7). (ref. ID; 4687)

Acanthocystis fortesca Nicholls, 1983 (ref. ID; 7206 original paper)

Diagnosis

Cells 8-10 um in diameter (fixed) with two types of scales. Spine scale a hollow shaft 0.15-0.2 um in diameter and 8-16 um long. Distal end of the spine ending bluntly in a whorl of 3-8 teeth usually of unequal size. The proximal end of the spine is attached to a broad thin membrane, obovoid in outline about 2 um wide and extending up the shaft of the spine 1.5-2.5 um. Base of the spine bent in the midregion of the membrane, creating a ladle-shaped depression. The proximal edge of the membrane is ornamented with 13-22 wavy subparallel ribs ca. 0.03-0.05 um wide and up to 0.7 um long. Plate-scales elliptical, 2.3-3x3.8-4.7 um, patternless except for marginal rim 0.05 um wide and a poorly developed median thickening about 0.1 um wide and 1.2 um long. (ref. ID; 7206)

Remarks

Acanthocystis fortesca is similar to A. pantopodeoides sp. nov. in the structure of the spine-scales. There are clear differences, however, which justify their separation at the species level. The ratio of spine length to cell diameter and the spine shaft diameter is about two times greater in A. pantopodeoides. The shape of the membrane on the spine base of A. fortesca is obovoid in outline compared to the truncate-spatulate shape of the corresponding structure in A. pantopodeoides. Other differences, such as in the shape of the plate-scales, are of lesser importance. (ref. ID; 7206)

Type material

Type from Fortescue Lake (44 degrees 50'N, 78 degrees 26'W) collected 23 April 1982 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0472), Ottawa. (ref. ID; 7206)

Acanthocystis granulata Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 35-40 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales, 10-13 um long, bipartite, consisting of shaft and base-plate. Shaft, 0.19 um thick, cylindrical, slightly tapering, distal end with 4 tiny marginal teeth. Shaft seated eccentrically on a heart-shaped base-plate, sometimes with slightly irregular outline. Periphery with a narrow rim. Ornamentation consists of an axial thickening, surrounded by a distinct pattern of radial slits, each ca. 0.27 um long and up to 0.03 um wide, located about midway between median thickening and rim of the scale. Small granules are scattered all over the surface, sometimes regularly arranged in radial rows. (ref. ID; 4724)

Remarks

A. granulata is easily distinguished from closely related A. pertusa by the presence of numerous granules on the plate scales, the less distinctly developed radial slits, which are located midway between the median thickening and the marginal rim. In A. pertusa these are close to the median thickening. A. granulata has so far only been observed in samples from the Banado Cruces. (ref. ID; 4724)

Etymology

From the Latin granulatus, with many little granules. (ref. ID; 4724)

Type slide

Type specimens collected 14 September 1979 from the Banado Cruces, southern Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.15). (ref. ID; 4724)

Acanthocystis heterospina Nicholls, 1983 (ref. ID; 7206 original paper)

See

Acanthocystis penardi (ref. ID; 4724)

Diagnosis

Cells 30-40 um in diameter; axopodia markedly beaded and rarely longer than the longest spine-scales. Scales of three types. Plate-scales elliptical 2.2-3.5x4-5.5 um, patternless except for a marginal rim which is sometimes poorly developed or lacking. Spine-scales of two types, differing only in size and consisting of a hollow cylindrical shaft seated on a circular base plate, 1-2 um in diameter. Shaft of the smaller spines ca. 0.25 um thick and up to 15 um long; large spines ca. 0.5 um thick and up to 25 um long. Both large and small spine-scales show a slight flaring at their apices and terminate in a row of 8-12 well-developed marginal teeth. (ref. ID; 7206)

Remarks

The large size of the cell and its spine-scales of two sizes permits identification with the light microscope. Only A. turfacea is comparable in size with two types of spine-scales but the bifurcate apices of its spines are easily distinguished from those of A. heterospina with the light microscope. Acanthocystis heterospina is possibly the same species which Penard (1904) assigned to A. spinifera Greeff. The two kinds of spine-scales set this species quite apart from A. spinifera, however (see also Wailes 1921, pp.54-55), and a new name is necessary. (ref. ID; 7206)

Type material

Type from West Twin Lake (44 degrees 39'N, 77 degrees 54'W) collected 24 April 1979 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0473), Ottawa. (ref. ID; 7206)

Acanthocystis kilianii Durrschmidt, 1987 (ref. ID; 4725 original paper) or 1985 (ref. ID; 4731)

Diagnosis

Periplast 25-40 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. Spine scales 5-10 um long, usually conspicuously curved outwards in the proximal quarter of their length. They consist of shaft, lateral wings and basal wings. The shaft is hollow, 0.23 um thick throughout, abruptly cut off at the apex at right angles without taper, basally terminating with a "shovel-lie" structure formed by the wings. There are two lateral wings in an almost V-form arrangement relative to the main axes of the shafts and a basal wing, which spreads between the ventral edges of the lateral wings. The lateral wings are 4.8-8.0 um long, accompanying 2/3 of the shaft length. They taper distally. Cross ribs are present on the lateral wings and on the basal wing. Plate scales, 2.6-4.3x2.1-3.2 um, are ovoid or elliptical, patternless, except for a subvisible axial thickening. (ref. ID; 4725)

Descriptions

The scales of A. kilianii observed were very similar to those described by Durrschmidt (1987). The spine scales were 5.6-9.0 um long, with lateral wings tapering distally and extending two thirds the length of the shaft, the shafts curving outwards in the proximal quarter of their length terminating in a blunt apex. The plate scales were more or less ovoid, 3.2-3.3x1.9-1.95 um, and patternless except for a slight axial thickening. (ref. ID; 4731)

Remarks

A. kilianii bears some likeness to A. pantopodeoides Nicholls (1983, syn. A. cuneiformis Durrschmidt 1985) and A. fortesca Nicholls (1983), having ribs on the basal wings, and non-tapering shafts. Distinguishing features are the longer and gradually tapering lateral wings, the shorter shafts, and the patternless plate scales. A. kilianii is also similar to A. erinaceoides especially as regards the wedge-like shape of the spine scales basis. To distinguish between both species offers no problems. The most useful characteristics are the absence of any kind of ribs on the wings, the tapering shafts, and the presence of a central swelling on the plate scales. However, EM is necessary for reliable identification. (ref. ID; 4725)

Etymology

In honour of Prof. Dr. E. Kilian, Justus Liebig University Giessen. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 14 September 1979 from the Banado Rio Cruces, Chile, and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.3). (ref. ID; 4725)

Acanthocystis latimarginalis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplasts, 25 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales spoon-shaped, consisting of shaft, lateral wings and basal wing. Shaft, 3-4 um long and 0.1 um thick, cylindrical, non-tapering apically crenulated or abruptly cut off. Proximately, the shaft carries 2 smooth lateral wings in an almost V-form arrangement relative to the main axes and a basal wing, which spread between the ventral edges of the lateral wings. The proximal shaft end is slightly curved outwards. Plate scales are elliptical or ovoid, 2-2.5x1.3-1.6 um, bordered by a broad radially striated rim, which reaches its max. thickness near the inner edge of this rim. The distinctly denser appearance in TEM shows that this structure is hollow. The central area is smooth, except for a dark central line (axial thickening?). (ref. ID; 4725)

Remarks

A. latimarginalis most closely resembles A. striata Nicholls (1983) from Canada. Both species are conspicuous for their broad radially striated rim surrounding the depressed central part of the plate scales. However, those of A. striata have additional ribs in this area as well as on the wings of the spine scales, whereas A. latimarginalis lacks ribs on both structures. Finds of single scales suggest that the whole group of organisms exists with similar plate scales. (ref. ID; 4725)

Etymology

From the Latin latimarginalis, with broad margin. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 7 March 1983 from Tissa Lake, Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.17). (ref. ID; 4725)

Acanthocystis myriospina Penard, 1890 (ref. ID; 3541, 3691, 4687) reported year? (ref. ID; 1334, 1923, 7206)

Synonym

Acanthocystis trifurca Nicholls, 1983 (ref. ID; 4710)

Descriptions

This species is provided with long, tapering, very numerous spines. (ref. ID; 1923)
Periplast, 10-45 m in diameter (measurement based on whole mount), covered by 2 types of siliceous scales. Details of protoplast unknown. Plate scales, 2.7-3.5x1.5-2.2 um, oviform to ellipsoidal. They are thin, with a sometimes blurred central ridge. Spine scales of only one kind, 3.5 to 16 um long, commonly extraordinarily numerous, with long, thin tubular shafts, plate-like bases (0.5-0.7 um in diameter) and tridentate distal ends. The shaft narrows slightly towards its distal end. (ref. ID; 4687)
Spine scales were 3.6-9.8 um in length with tips 0.12-0.15 um long, and a base 0.57-0.90 um in diameter. (ref. ID; 4710)

Remarks

A. myriospina was described by Penard (1890) from material collected from stagnant waters in the vicinity of Wiesbaden, F.R.G. Apart from being somewhat larger -45 um (measurement based on whole mounts) versus 30 um- the most striking similarity between Penard's diagnosis and the periplasts found in Chile are the extraordinary numerous spine scales, which are long (about 2/3 or more of the cell diameter according to Penard) and delicate, straight or rarely curved. However, the distal ends of the spine scales are not tapering or pointed, but have three short teeth. This feature, however, is only visible by electron microscopy. Beside those periplasts typical for A. myriospina, there have been others which should also be identified with A. myriospina as regards their identical scale structure. However, these derivate from the specific description in that their spine scales are less numerous and the length of the shaft is considerably variable among single specimens from 3.5-16 um. This suggests that these characteristics are of limited or no value for specific identification, in contrast to the scale structure itself. As the type material, if it has been deposited at all, has been lost, as inquiries at the following institutions revealed (British Museum, London; Museum D'Histoire Naturelle, Geneva; The Royal Microscopical Society, London; Museum National d'Histoire Naturelle, Paris), and as the type localities have probably been destroyed by urbanization, it appears necessary to chose a neotype in order to end this taxonomic uncertainty. (ref. ID; 4687)
Specimens from Pond No. 5 have been tentatively assinged to this species on the basis of their numerous very thin and delicate spine-scales. Cell size and spine length of the Ontario specimens agree with those given by Penard (1904) and Wailes (1921). Electron microscopy shows the shaft of the spine-scales is hollow and only 0.15-0.18 um diameter throughout. The apex is abruptly cut off with a minutely serrated margin. The shaft of the spine is seated on a circular base plate in the shape of a cone 1.5-2.3 um in diameter. Although the edges of several plate-scales were seen around the borders of some dried specimens, none of the preparations resulted in a clear view of intact plate-scales. (ref. ID; 7206)

Habitat of the neotypus

Small forest pond near Entre Lagos on the Puyehue pass road, loc. 5. Collected on July 20, 1981. (ref. ID; 4687)

Neotype slide

Deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:2). (ref. ID; 4687)

Acanthocystis nichollsi Siemensma & Roijackers, 1988 (ref. ID; 4745 original paper)

Comments

This new name is proposed for the species identified by Nicholls (1983) as Acanthocystis pectinata, Nicholls (1983) gave an emended diagnosis of A. pectinata, but this specimens differ from the original diagnosis of this species. A. pectinata is characterised by the presence of numerous short spine-scales, all of the same length (Penard 1889, 1904) and a scanty number of long spine-scales (Rainer 1968). Rainer emphasised that the presence of a very small number of long spine-scales is a specific character, which was confirmed by Siemensma (1981). The Canadian specimens deviate clearly from the European specimens in having many long spine-scales, and Nicholls (1983) observed all intermediate lengths between long and short spine-scales. Therefore, the light microscopic appearance of these specimens does not correspond well with the original description of A. pectinata nor with the emendation by Rainer (1968). The surface of the plate-scales of the Canadian specimens is smooth, whereas the specimens we observed from several localities throughout the Netherlands, and which we consider to be identical with A. pectinata, all have granulated plate-scales. In TEM, the plate-scales of A. nichollsi have radial slits, which are lacking in A. pectinata as now defined. Acanthocystis nichollsi closely resembles A. polymorpha Durrschmidt, 1985, the plate-scales of which lack any granules or slits. (ref. ID; 4745)

Acanthocystis ovata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast very small, 5-10 um in diameter (measurement based on whole mount): details of protoplast unknown. Scales of two types. Spine scales 1.2 to 1.5 um long and 1.07 um broad, oviform in outline with delicate, regularly-spaced ribs. These radiate from the shaft of the outer margin. The shaft is vestigially developed and visible only as a dark line. The area around the shaft is a slightly concave depression. The lateral wings and basal wing join on to the oval form of the spine scales. The plate scales are elliptical, 1.5x0.6 um, patternless except for a narrow rim and an axial thickening. (ref. ID; 4725)

Remarks

A. ovata is by far the smallest Acanthocystis species I found during this study. These are some relationships to A. formosa Durrschmidt (1985) and A. veliformis (op. cit.). As in these species, the shaft is reduced and the elaboration of the lateral and basal wings favoured. The area around the shaft base is depressed concavely. Despite this general similarity, A. ovata is clearly distinguished by its faintly developed rib pattern and the smallness of the periplast and the scales. (ref. ID; 4725)

Etymology

From the Latin ovatus, ovate. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 7 September 1979 from a swamp (nadi) near Villariica, Province Cautin, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.12). (ref. ID; 4725)

Acanthocystis paliformis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast 8-15 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. The spine scales are almost spade-form, 4.5 um long and max. 2.3 um breadth. The shaft is reduced to a short hollow ridge of varying breadth, ending distally with a blunt apex. The lateral wings and the basal wing are narrow rimmed and joined to the shade-like form of the spine scales. The wings on either side of the shaft run almost parallel to it but then narrow abruptly and terminate subapically. The area around the "shaft base" is depressed to a concavity. The plate scales, 2.5x1.5 um, are elliptical or ovoid. The scales are thin and narrow-rimmed. The central swelling is rudimentarily developed and slightly shifted to the smaller pole of the scale. (ref. ID; 4725)

Remarks

A. paliformis is conspicuous by virtue of the remarkable similarity between the plate and spine scales. It appears that the structure, which forms the shaft in the spine scales might be identical with the central swelling in the plate scales. Other corresponding points are the concave depression at the basal end of the shaft and the way the width of the shaft and the central swelling varies in both scale types. Also in A. erinaceoides scales have been found which might demonstrate different stages between plate and spine scales. (Patterson and Durrschmidt, in prep.). A. paliformis is related to A. erinaceoides and A. pinnata not only because of the smooth wings but also because of the elaboration of a central swelling. As far as the shape of the spine scale is concerned, A. paliformis might be placed between A. pinnata and A. foliacea, as the shaft/wing relation is smaller than in A. pinnata and the plate scales still reveal a central swelling, although a reduced one (lacking in A. foliacea). (ref. ID; 4725)

Etymology

From the Latin paliformis, spade-like. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected on 2 July 1981 from Lake Lanalhue, Province Bio-Bio, Chile and filed with the British Museum, Protozoa Section (accession no. 1985.1.30.6). (ref. ID; 4725)

Acanthocystis pantopoda Penard, 1904 (ref. ID; 3541, 3691 original paper, 4724)

Emended diagnosis

The original description by Penard (1904) gives an almost complete account of the cell structure visible in LM, which agrees well with the specimens found in Sri Lanka. The new taxonomy of the genus based on EM of the scale structure necessitates an expanded description. Periplast, ca. 60-70 um in diameter, with two kinds of scales. Spine scales straight or slightly curved, 25-30 um long, tapering slightly to a blunt apex with a toothed margin of 6 triangular teeth. Shaft, cylindrical and hollow, the sides are of irregular thickness (ca. 0.5 um thick), basal sometimes with siliceous nodules. Base of the spine seated eccentrically on a heart-shaped base-plate, 1.5 um in diameter. Plate scale patternless, elongated elliptical with a distinct median constriction, 3.5-4.0x2.3-2.5 um. (ref. ID; 4724)

Remarks

This species is easily recognized, with light- and electron microscopy, by the shape and size of the periplast and the extremely long, strongly built, spine scales, 1.5-2 times the cell diameter in length. A. pantopoda is distinguished from A. cordiformis (this paper) on the basis of the length and breadth of the spine scales and the appearance of the plate scales, which are thicker than those of A. cordiformis spp. According to its ecological demands, A. pantopoda may be possibly considered polythermal, as its occurrence in the tropics and during summer (Rainer 1968) in Central Europe indicates. (ref. ID; 4724)

Acanthocystis pantopodeoides Nicholls, 1983 (ref. ID; 4745, 7206 original paper)

See

Pterocystis fortesca (ref. ID; 4745)

Diagnosis

Cells 10-12 um in diameter (fixed) with two types of scales. Spine-scales a hollow shaft 15-24 um long and 0.3-0.4 um wide throughout, ending in a marginal whorl of 4-10 teeth usually of unequal size. The base of the spine shaft is bent and fused to a membrane truncate-spatulate in shape 2-3 um wide at the base and extending along the shaft 2-4 um. The membrane forms two wings on either side of the base of the spine; these are angled to form a wedge-shape structure which is closed off at the proximal end by a rounded membrane patterned with a series of 15-25 subparallel ribs ca. 0.05 um wide. Plate-scales oblong, 1.7-2.3x3.5-4.5 um, patternless except for a marginal rim 0.03 um wide and a poorly developed median ridge or fold about 0.1 um wide and 2.4-3.2 um long. (ref. ID; 7206)

Remarks

The characteristically straight and long (relative to the protoplast) spine-scales impart a general outline to the cell of A. pantopodeoides not unlike that of A. pantopoda Penard. However, Penard (1904) showed the spine bases of A. pantopoda were of the kind known for A. turfacea and other related species with base "in tete de clou." Penard was able to identify structures such as the delicate plate-scales of this and other species, which in my experience, are more difficult to resolve with the light microscope than the bases of the spine-scales. The similar triangular wedge-shaped membranes of the spine bases of A. erinaceoides and A. pantopodeoides can be seen clearly with the light microscope and hence must be considered to be distinct from the structure Penard (1904) described for A. pantopoda. Other differences between A. pantopoda and A. pantopodeoides, of lesser taxonomic importance than scale structure, include apparent size differences of both the cell and spines; the former species is nearly two times larger than A. pantopodeoides. (ref. ID; 7206)

Type material

Type from Memoir Lake (47 degrees 39'N, 82 degrees 59'W) collected 6 June, 1979 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0474), Ottawa. (ref. ID; 7206)

Acanthocystis pectinata Penard, 1889 (ref. ID; 3541, 3691, 4724) reported author and year? (ref. ID; 4009), emend. Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper), emend. Nicholls, 1983 (ref. ID; 7206 redescribed paper)

Emended diagnosis

Cells (10-) 15-20 (-23) um in diameter with two kinds of scales. Spine-scales straight or slightly curved, 2-12 um long. Shaft of spine hollow, 0.2-0.3 um in diameter. Apex of spine separated into (usually) six arms and interconnected by a flaring of the distal portion of the spine shaft. Flaring of the spine terminus more pronounced in short spines (2-4 um long) than in long spines; width of the distal flare up to 1.5 um. Base of the spine in the form of a shallow inverted cup 0.6-0.9 um in diameter. Plate-scales 1.5-2.2x2.5-3.8 um; perifery usually with a thickened rim 0.02-0.04 um wide. Plate-scale ornamentation consists of an axal thickening or ridge oriented longitudinally in the middle of the scale and surrounded by a more or less well-developed pattern of radial slits each ca. 0.1-0.2 um long and up to 0.05 um wide located about midway between the median ridge and the rim of the scale. Spine-scales over the whole range in length (2-12 um) have been found; but, more commonly, the spine-scales on an individual cell fall into either the long (8-12 um) or short (2-4 um) categories. As in A. turfacea the degree of flaring of the spine apex of A. pectinata is inversely related to the spine length. (ref. ID; 7206)

Emended description

Cell diameter 15-20 um. These are two kinds of spine-scales: short and long spine-scales. The short spine-scales are all of the same length, 2.1-3.1 um long. Their shaft is cylindrical, hollow and straight, 0.25 um thick. The apex is cup-shaped, 0.8-1.4 um wide and has 4-6 long, diverging sharp teeth, interconnected by a thin membrane. The basal plate is 0.43-1.2 um in diameter, conical, circular, with a fairly thick margin. The long spine-scales are not abundantly present. They are 6.0-10.2 um long with the apex terminating in 2-3 short teeth. No intermediate lengths between the short and the long spine-scales were observed. The plate-scales are 1.6-2.5x1.3-1.6 um, oblong to slightly ovoid with faintly concave sides; they have a broad marginal are ornamented with a pattern of small granules arranged in more or less concentric or radial rows. Similar plate-scales were observed by Durrschmidt (1987) and assinged to a new subspecies, A. pectinata ceylanica. (ref. ID; 4745)

Acanthocystis pectinata Penard, 1898 (1889 misspelling?) ssp. ceylanica Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

A. pectinata ssp. ceylanica is distinguished from A. pectinata ssp. pectinata in that it has non-slitted plate scales, provided with concentric rows of irregularly placed minute dots. (ref. ID; 4724)

Remarks

A. pectinata ssp. ceylanica was common in the type habitat. Despite intense search for slitted plate scales, no cell with both types of plate scales was questionable as indicated by Nicholls' Fig.59 (1983). (ref. ID; 4724).

Etymology

From its occurrence in Sri Lanka. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected 6 March 1983 from a small pond near Batticaloa, E. Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.6). (ref. ID; 4724)

Acanthocystis pectinata Penard, 1889 ssp. malayensis Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

A. pectinata ssp. malayensis differs from A. pectinata ssp. pectinata in that the plate scales are elongated elliptical, slightly curved and with broad radial slits, 0.35 um long and 0.07-0.08 um broad. These are vestigial around the scale ends. The axial thickening is pronounced. (ref. ID; 4724)

Remarks

A. pectinata ssp. malayensis has so far only been observed in Malaysian waters. The plate scales resemble the description of A. quadrifurca Nicholls (1983, syn. A. clathrara Durrschmidt 1985) but both taxa are clearly distinguished by the shape of the spine scales. The presence of specimens with identical spine scales, but with different plate scales, seems to be widely distributed in Acanthocystis. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected 7 August 1982 from a roadside ditch near Kota Tinggi, Malaysia and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.7). (ref. ID; 4724)

Acanthocystis penardi Wailes, 1925 (ref. ID; 3541, 4724) reported author and year? (ref. ID; 4009)

Synonym

Acanthocystis heterospina Nicholls, 1983 (ref. ID; 4724); Acanthocystis spinifera Penard, 1904 nec Greeff, 1869 (ref. ID; 3541, 4724)

Descriptions

The large size of this species together with its investiture of two types of truncate spine scales contribute to its easy identification by light microscopy. (ref. ID; 4724)

Comments

Penard (1904) gives a detailed description together with excellent drawings but inadvertently attributes it to A. spinifera Greeff (1869). Wailes (1921, 1925) recognized that A. spinifera in Penard (1904) is not identical with A. spinifera Greeff and described this species as A. penardi. Re-examination of Penard's original slides (no. 523, 626, Museum D'Histoire Naturelle, Geneva) confirms Wailes' view. Siemensma (1981) was the first who studied the fine structure of the spine scales by electron microscopy. Characteristic of both spine scales types are the slightly flared and corrugated apices, which terminate in a row of about 8-10 (14) terminal teeth. Identical spine scales are found in A. heterospina Nicholls (Nicholls 1983), which has been described by light- and electron microscopy from Canada. On account of their general similarity in cell shape and scale structure, it appears reasonable to treat A. heterospina as synonymous with A. penardi. (ref. ID; 4724)

Acanthocystis penardi Wailes, 1925 ssp. pusilla Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 25-35 um in diameter (measurement based on whole mount), with 2 types of scales. Details of protoplast unknown. Plate scales, 2.7-3.0 x 1.1 to 1.4 um, pear-shaped or more rarely elliptical with a median constriction. A short axial thickening is present together with numerous dots, arranged in more or less concentric circles. Spine scales, 3.9-6.6 um long, consist of a hollow cylindrical shaft (ca. 0.25 um in diameter) protruding from a circular base-plate (1.0-1.5 um in diameter). Distal ends with a slight flaring and 4-7 marginal teeth. (ref. ID; 4724)

Remarks

A. penardi ssp. pusilla is distinguished from genuine A. penardi by the presence of only one type of spine scale, by the longer and less numerous apical teeth (4-7 as compared to 8-14) and on the basis of considerably smaller cells and scales. However, one cannot preclude the possibility that future investigations may reveal that the differences noted only indicate the presence of different clones. But this is a constant difficulty in the taxonomy in the case of predominantly asexual reproduction organisms like the Centrohelids. For the moment, however, it seems appropriate to deal with these two types at subspecies level. Because of the general similarity between species like A. penardi ssp. pusilla, A. myriospina Penard sensu Nicholls (1983), A. rotunda Nicholls (1983) or A. perpusilla Petersen and Hansen (1960) a.o. in light microscopy, EM is required for reliable identification. The most distinctive characteristics of A. penardi ssp. pusilla are the shape of the spine scale apices and the form and ornamentation of the plate scales. (ref. ID; 4724)

Etymology

From the Latin pusilla, small. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected on July 6, 1981 from a paludal forest near Puerto Varas, southern Chile and filed with the British Museum London, Protozoa Section (accession no. 1981.12.17.4). (ref. ID; 4724)

Acanthocystis perpusilla Petersen & Hansen, 1960 (ref. ID; 3541, 4687)

Remarks

A. perpusilla is one of the few Acanthocystis species of which EM micrographs of the siliceous scales exist. The fine structure of the plate and spine scales of the Chilean specimens agrees with Petersen and Hansen's description, although discrepancies in the dimensions of the periplasts and the spine scales exist between the Chilean and the Danish material. Many diverging forms have been observed, of which it is unknown whether the noticeable differences especially regarding the shape of the spine scales as well as the relation between shaft length and cell diameter should be considered as infraspecific variation of indicate the presence of different species. (ref. ID; 4687)

Acanthocystis pertusa Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 50-60 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales, 15-25 um long, consisting of shaft and base-plate. Shaft, 0.2 um thick, apparently solid or only partly hollow. Spines slightly tapering towards the distal end, apex with 4 marginal teeth. Shaft seated eccentrically to a heart-shaped base-plate, 1.4 um in diameter. Plate scales, 5.6-6x3.3 um, elliptical, sometimes slightly curved. Scale ornamentation consists of numerous radial slits, 0.56 um long and 0.07-0.14 um wide, directly situated on both sides of the axial thickening, which is 3.0 um long. Rest of the scale smooth. (ref. ID; 4724)

Remarks

It is not possible to distinguish between A. granulata and A. pertusa with reference to the spine scales alone, though these of A. pertusa are 1/4 longer than those of A. granulata. The slit-pattern on the otherwise smooth plate scales, is the most characteristics feature of A. pertusa and plate scales are about twice as large as those of A. granulata. A. pertusa is the fifth taxon of the genus Acanthocystis with slitted plate scales to be reported and the second with heart-shaped spine scales. (ref. ID; 4724)

Etymology

From the Latin pertusus, having holes or slits. (ref. ID; 4724)

Type slide

Type specimens collected 7 March 1983 from Tissa Lake, southern Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.16). (ref. ID; 4724)

Acanthocystis pinnata Nicholls, 1983 (ref. ID; 4725, 7206 original paper)

Diagnosis

Cells 5-8 um in diameter (fixed) with two types of scales. Spine-scales, a hollow shaft 3.5-6 um long, 0.13-0.2 um in diameter in the midregion and tapering to a bluntly rounded apex. Base of the spine attached to a broad membrane which is flared into two lateral lobes then tapers distally along the spine shaft to terminate subapically. The base of the spine shaft is bent, creating a depression in the membrane and a ladle-like appearance to the basal structure of the spine. Plate-scales elliptical 1.3-1.7x2-2.5 um, each with a well developed rib (0.1-0.2x1-1.4 um) which tapers to both ends and occupies the median one-half to two-thirds of the long axis of the scale. (ref. ID; 7206)

Remarks

Acanthocystis pinnata is closest to A. erinaceoides but differs from it mainly in the structure of the spine-scales and its much smaller size. (ref. ID; 7206)

Type material

Type from Pond No.1 (44 degrees 48'02"N, 78 degrees 29'W) collected May 5, 1981 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0475), Ottawa. (ref. ID; 7206)

Acanthocystis plumosa Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast, 20-30 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. The spine scales are 7-12 um long, of feature-like appearance. The shaft, 0.01 um in diameter, is cylindrical, hollow, ending apically with a blunt or abruptly cut off apex. The lateral wings are continued along 2/3 of the shaft, reaching their maximum breadth in the lower half of the spine scale. From here towards the proximal end, they are closely anchylosed with the basal wing and after considerably narrowing, form a patternless hollow stalk. The basal part of the stalk is foot-shaped. The lateral wings are ornamented with thin, delicate ribs which run from the shaft to the outer margin transverselly or obliquely. Plate scales, 3.0-3.7x1.9-2.1 um, ovoid or elliptical or sometimes asymmetrical. They are thin with deeply concave middle parts, elevated submarginal parts and slightly inflexed margins with a narrow rim. The axial thickening is slightly shifted to the smaller end of the scale. (ref. ID; 4725)

Remarks

A. plumosa is closely related to A. pulchra. The major distinctive characteristic is the long, wingless distal shaft part. Spine scales with similar foot-shaped bases are also found in one form of A. pulchra which might be intermediary between A. plumosa and genuine A. pulchra. (ref. ID; 4725)

Etymology

From the Latin plumosus, feathery. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 7 September 1979 from a swamp (nadi) near Villarrica, Province Cautin, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.13). (ref. ID; 4725)

Acanthocystis polymorpha Durrschmidt, 1985 (ref. ID; 4687 original paper)

Diagnosis

Periplast 50-100 um in diameter (measurement based on LM and whole mount). Scales of 2 types. Protoplast unknown, all cells with photosynthetic symbionts as revealed by LM. Plate scales arranged in one to several compact layers, 4-5.5x2.1-3.3 um, ellipsoidal or ovoid, commonly with an approximately median narrowing. Plate scales asymmetrically or triangularly shaped have been observed, too. Usually they are uniformly thick without a clearly defined central ridge. Dorsal and ventral surfaces are smooth, sometimes revealing a delicate zonation caused by the successive apposition of scale material. Spine scales of two kinds, all with tubular shafts and round plate-like bases. These base-plates possess ventrally a central annular depression and slightly rimmed margins. One kind (i) is 15-30 um long, shaft not tapering, with slightly dilated distal ends, distal margins regularly indented. Second kind (ii) usually half as long as (i), 5-10 um, provided distally with curiously "funnel-like" ends, caused by a considerably broadened shaft. There are 5-8 radially diverging ridges of which each terminates in a small pointed tooth. The scale material between has an slightly inwardly curved edge. The length of these spine scales varies between such extremes that there is sometimes even no shaft at all and the "funnel-like" distal ends are directly attached to the base-plates. Thransitional spine scales between kinds (i) and (ii) are also present. (ref. ID; 4687)

Remarks

A. polymorpha bears some likeness to A. turfacea, for instance, in the possession of more than one kind of spine scales, in their similar base-plates, and in their tubular shafts. Apart from the type locality, A. polymorpha was also frequent in other Sphagnum bogs on Chiloe Islands, e.g. Sphagnum bog near Manao. It seems to inhabit especially acid, extremely oligotrophic, clear waters low mineral content. Single spine scales, perhaps belonging to A. polymorpha, have been published earlier by Takahashi (1959) from Japan, as microplankton no. 8 from Arasawa-dam. (ref. ID; 4687)

Etymology

The epithet "polymorpha" refers to the polymorphic spine and plate scales. (ref. ID; 4687)

Type locality

Pools in a Sphagnum magellanicum bog (loc. 8), 12 km north of Castro, Island of Chiloe/Chile. Collected July 13, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:1). (ref. ID; 4687)

Acanthocystis pteromorphos Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast small, 10-15 um in diameter (measurement based on whole mount): details of protoplast unknown. Spine scales 2-2.5 um long, consisting of shaft, lateral wings and basal wing. Shaft, 0.09 um in diameter, slightly bent and hollow. Apex of the shaft abruptly cut off at right angles without taper. Lateral wings max. 0.4 um broad, mutually positioned at an angle of 180 degrees, taper distally along the spine shaft to terminate subapically. Horizontally directed slits are present irregularly. The basal with is almost rectangular and smooth. Plate scales, 2.1x1.2 um, are elliptical, patternless except for a faintly elaborated axial thickening. (ref. ID; 4725)

Remarks

As far as the smooth wings are concerned, A. pteromorphos belongs in the line A. erinaceoides, A. pinnata and A. foliacea. It is considered to represent the non-ribbed counterpart of A. kilianii with which it corresponds in the open end of the shaft and in the long, gradually tapering lateral wings. (ref. ID; 4725)

Etymology

From the Greek, wing-shaped. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 14 September 1979 from the Banado Cruces, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.11). (ref. ID; 4725)

Acanthocystis pulchra Durrschmidt, 1985 (ref. ID; 4687 original paper, 4725)

Diagnosis

Periplast, 20-30 um in diameter (measurement based on whole mount) covered with 2 types of scales. Details of protoplast unknown. Plate scales, 3.0-3.3x1.7-2.0 um, are ovoid to ellipsoidal or sometimes asymmetrical. They are thin with deeply concave middle parts, elevated submarginal parts and slightly inflexed margins. They are patternless, the central ridge indicated only as a slightly darker line. The spine scales are rather numerous, 3.0-4.0 um long, max. 3.1-3.8 um broad, of almost funnel- or calyx-like appearance. The shaft is reduced to a dark narrow ridge, probably hollow, because of its less dense centre. The lateral wings are continued along the whole length of the shaft, reaching their maximum breadth in the middle distance of the scale. From here toward the proximal end they are closely anchylosed with the basal wing as, after considerable narrowing, form a patternless hollow stalk, which can be long and slender or short and stumpy. Distally the scales are of differing lengths; commonly the front parts are shorter and slightly curved outwards, and the rear parts straighter, reaching their max. length near the distal shaft end. The lateral wings are ornamented by thin delicate ribs, which run from the shaft to the outer margin transversally or obliquely. Ribs are also present on the front part of the calyx but here they run inwards from the outer margin. (ref. ID; 4687)

Remarks

This species is conspicuous by virtue of its characteristic closely fitting periplasts and the funnel or calyx-like spine scales. At first sight these do not bear much resemblance to Acanthocystis, and for this reason classification is mainly based on the structure of the plate scales. There is also a suggestive resemblance to Raphidocystis species, e.g. R. glutinosa Penard, 1904, but due to the lack of examination of living tissue, this cannot be determined for certain. Nevertheless, there are some relationships to species described earlier in this paper, e.g. A. foliacea, and A. cuneiformis. As in A. foliacea, the shaft is reduced and the elaboration of lateral and basal wings favoured. There is also a stalk, but this takes up half of the spine scale in A. pulchra. By reason of the broad winged scales, the development of a stalk enables more spine scales to be situated on the periplasts. There is also a presumed resemblance despite all differences between A. pulchra and A. cuneiformis concerning the rib-pattern of the spine scales. Like the basal wing in A. cuneiformis, the front part is ornamented in A. pulchra by ribs. The cross-ribs of the lateral wings, present in A. cuneiformis only in vestiges, also indicate the relation between these two species. (ref. ID; 4687)

Etymology

The specific epithet "pulchra" refers to the beautiful spine scales. (ref. ID; 4687)

Type locality

Swamp on the left-hand side of the southbound Pan American Highway, 42 km south of Puerto Montt, loc. 7. Collected on July 17, 1981. (ref. ID; 4687)

Type slide

Holotype deposited in the British Museum London, Protozoa Section (accession no. 1983:1:31:6). (ref. ID; 4687)

Acanthocystis pyriformis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast 8-15 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. Spine scales almost pear-shaped, 1.5-2.0 um long. The shaft 1.4 um long, 0.06 um thick, is hollow, distal half without wings and tapering to a blunt apex. The lateral wings and the basal wing join to the peak-like appearance. The wings are smooth, their outer edge is slightly curved inwards. The area around the shaft base is depressed concavely, giving the impression of a scoop. Plate scales, elongated elliptical ovoid, 1.4-1.6 um with a narrow peripheral rim and a central swelling, sometimes developed only as an axial thickening. (ref. ID; 4725)

Remarks

A. pyriformis most closely resembles A. paliformis but differs in the form and size of the spine scales and in the appearance of the plate scales. Also in A. pyriformis the plate scales reveal a central swelling, which demonstrates the close relationship of this species to A. paliformis and A. erinaceoides. The gradual reduction of the central swelling can be traced back from A. erinaceoides over A. pinnata, A. paliformis to A. pyriformis and finally perhaps to A. foliacea. During this process the shaft becomes more and more reduced. It is, therefore, supposed that both characteristics are controlled by the same gene centre. The only species which does not fit into this scheme is A. pteromorphos, which also deviates in having non-tapering shafts. Like in A. paliformis, A. pyriformis shows no variations in scale morphology despite the enormous geographical distances involved. (ref. ID; 4725)

Etymology

From the Latin pyriformis, pear-shaped. (ref. ID; 4725)

Type slide

Type specimen found in a water sample from a roadside ditch near Lake Caburga, Chile, collected 7 September 1979 and filed with the British Museum, Protozoa Section (accession no. 1985.1.30.7). (ref. ID; 4725)

Acanthocystis quadrifurca Nicholls, 1983 (ref. ID; 7206 original paper)

Diagnosis

Scales of two types; plate-scales elliptical to oblong 1.2-2.0x1.8-3.5 um consisting of an oblong centrally positioned membrane with a thickened axial ridge and an outer rim 0.8 um wide connected to the central membrane by 20-30 radial ribs which are sometimes forked or branched. Spine-scales, a straight or slightly bent shaft 5-10 um long, 0.05-0.15 um in diameter and seated on a circular baseplate 0.8-1.2 um in diameter in the form of a shallow inverted cup. Ends of the spines separated into four flared arms about 0.1-0.2 um long which taper to a sharp point. (ref. ID; 7206)

Remarks

The spine-scales of this species might suggest some close relationship to A. trifurca sp. nov. at first; however, the main differences are in the spine shaft which is hollow with a three-pronged apex in A. trifurca but is solid with a four-pronged apex in A. quadrifurca. The plate-scales of A. quadrifurca with their striking "spoked wheel" pattern is very distinctive and cannot be confused with plate-scales of any other known Acanthocystis species. (ref. ID; 7206)

Type material

Type from Pond No. 3 (45 degrees 01'N, 79 degrees 38'05"W), collected August 19, 1981 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0476), Ottawa. (ref. ID; 7206)

Acanthocystis rasilis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast, 10-20 um in diameter (measurement based on whole mount), with two types of scales: details of protoplast unknown. Plate scales, 3.0-3.3x1.7-2.0 um, are elliptical and sometimes slightly curved. They are patternless, with a narrow peripheral rim and a faintly developed axial thickening. The spine scales are 3.0-4.0 um long without any special surface pattern and of almost funnel- or calyx-like appearance. The open ends are circular, 2.6-3.0 um in diameter and surrounded by a small narrow rim. The scales narrow abruptly to a 1.5 um long, slender tube with a small capitate base. A shaft, or vestiges of it, have never been detected. (ref. ID; 4725)

Remarks

A. rasilis is conspicuous by virtue of its closely fitting periplasts. As in A. pulchra Durrschmidt (1985), the spine scales remain attached to the plate scale layer, even during fixation and drying. The appearance of A. rasilis under light microscope resembles that of Raphidocystis glutinosa Penard (1904), especially in the shape and size of the periplast and the spine scales. EM micrographs of plate scales, described by Penard (1904) as "ecailles on baquettes, sans forme precise, tantentes" proved to be of identical structure to those of other species of Acanthocystis. Another feature, which also contradicts an identification with Raphidocystis is the absence of a second type of spine scales (S1-scale). Arguments for classifying these specimens with Raphidocystis may be seen in the complete absence of a shaft. The only so far known Raphidocystis species with smooth spine scales in R. glabra Durrschmidt (in Nicholls and Durrschmidt 1985), with which A. rasilis otherwise has very little in common. Funnel-shaped spine scales have also been reported in the genus Acanthocystis: A. pulchra. Despite the basic similarity, the spine scales of A. pulchra are easily distinguishable by their conspicuous rib-pattern and the vestigially-developed shaft, though both characteristics are only detectable under the electron microscope. As it remains uncertain on which of the species Penard based the original diagnosis of Raphidocystis glutinosa and as no type material has been deposited, a classification with one of these Acanthocystis species appears rather arbitrary. (ref. ID; 4725)

Etymology

From the Latin rasilis, smoothed. (ref. ID; 4725)

Type slide

Type specimen found in a water sample collected 20 July 1982 from a swamp in Buller Gorge, South Island/New Zealand and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.10). (ref. ID; 4725)

Acanthocystis rhytidos Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 35-40 um in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales, 9-12 um long, bipartite, consisting of shaft and base-plate. Shaft cylindrical, 0.19 um in diameter, presumably solid and slightly tapering towards the distal end, abrupt apically ending with 2-4 marginal teeth. Base-plate heart-shaped, 1.3 um in diameter. Plate scales, 3.8-4x2.2-2.6 um, elliptical or pear-shaped, ornamented by radially-arranged, branched furrows of different length. The area of the axial thickening and a narrow submarginal strip are smooth. (ref. ID; 4724)

Remarks

A. rhytidos most closely resembles A. granulata and A. pertusa, in having distinctly patterned plate scales along with bipartite spine scales with heart-shaped base-plates. The plate scales or A. rhytidos reveal no slits but a system of radially arranged brached furrows or little canals, which are only occasionally perforated. With regard to the possible evolution of the various plate scale types in Group B, one might say that A. cordiformis probably represents the basic scale type from which the furrowed (A. rhytidos), finely slitted (A. granulata, this paper) and large-slitted (A. pertusa, this paper) forms may have evolved progressively. (ref. ID; 4724)

Etymology

From the Greek, wrinkled. (ref. ID; 4724)

Type slide

Type specimens collected 4 July 1981 from a small pond 15 km north of Valdivia and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.14). (ref. ID; 4724)

Acanthocystis rotundata Nicholls, 1983 (ref. ID; 4724, 7206 original paper)

Diagnosis

Scales of two types. Spine-scales 3-12 um long, usually slightly bent in the proximal one-quarter to one-half of their length. Spine shaft hollow, 0.12-0.2 um in diameter, seated eccentrically at the base of a cleft in an ovate to circular base plate 1-1.3 um in diameter. Base plate with a marginal rim. Apex of the spine shaft abruptly cut off at right angles without taper but with 12-20 minute marignal rounded teeth about 0.015 um high. Plate-scales elliptical 2.5-3.5x1.5-2.5 um, patternless except for an axial thickening positioned in the middle of the scale about two-thirds the length of the scale and a maximum width of about 0.15 um in the midregion. (ref. ID; 7206)

Remarks

The base plates of the spine-scales of A. rotundata are similar to those of A. perpusilla Petersen & Hansen; however, A. perpusilla spines are only 3-4 um long and have a marked bifurcation at their apices. (ref. ID; 7206)

Type material

Type from Round Lake (45 degrees 00'N, 79 degrees 38'W), collected May 5, 1981 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0477), Ottawa. (ref. ID; 7206)

Acanthocystis rotundata Nicholls, 1983 ssp. rotoairense Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

A. rotundata ssp. rotoairense differs from A. rotundata in having larger periplasts (38-50 um in diameter, measurement based on whole mount), larger plate scales (4.5-5.0x2.5-3.0 um) with distinctly uneven surfaces, longer spine scales (14-18 um long) terminating apically with 4 minute teeth. (ref. ID; 4724)

Remarks

As in many other recently described Acanthocystis species the variability of A. rotundata is still completely unknown. From the large amount of material examined here, it is evident that almost all specimens from Chile, Malaysia, Sri Lanka and New Zealand agree with the scale dimensions given by Nicholls for A. rotundata. Only those specimens found in Lake Rotoaira differ in having conspicuously larger plate scales with uneven surfaces, longer spine scales with 4 teeth on the distal end. Those of A. rotundata are described as being "abruptly cut off at right angles... with 12-20 minute marginal rounded teeth" (Nicholls 1983). At present it is not possible to decide whether these differences in scale size and structure justfy the establishment of yet another Acanthocyctis species. For this reason it is described here on subspecific level. (ref. ID; 4724)

Etymology

From the type habitat, Lake Rotoaira. (ref. ID; 4724)

Type slide

Type specimens collected 16 July 1982 from Lake Rotoaira, 4.8 km SW of Mt. Pihanga, North Island, New Zealand and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.17). (ref. ID; 4724)

Acanthocystis scaposa Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, ca. 10 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. Plate scales, 1.2-1.5x0.6-0.8 um, are patternless, except for a vestigially developed axial thickening. Spine scales, (1.1) 1.9-2.3 (7.2) um long, consist of shaft, base-plate and lateral wings. Shaft narrow, non tubular, tapering to a blunt apex. Wings, ca. 0.08 um broad, to be found on either side of the shaft. They are broadest just beyond the base-plate but then narrow gradually towards the distal end of the shaft. Base-plate ca. 0.5 um in diameter, reniform or heart-shaped, surrounded by a narrow peripheral rim. (ref. ID; 4724)

Remarks

A. scaposa is remarkable in that two otherwise always separate characteristics are combined in its spine scales: lateral wings and heart-shaped base-plates. Variation with in A. scaposa is most noticeable with regard to the size of the spine scales. Whereas those from the majority of the Chilean habitats and from Sri Lanka vary from 1.9 to 2.3 um, those from a swamp near Puerto Montt/Chile are 7.2 um long. There is, however, no reason to believe that this difference should be considered anything but infraspecific variation. It may indicate the presence of different clones, or different stages in the cell or life cycle. (ref. ID; 4724)

Etymology

From the Latin scaposa, with shaft. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected on September 14, 1979 from the Banado Cruces, southern Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.1). (ref. ID; 4724)

Acanthocystis scaposa Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, ca. 10 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. Plate scales, 1.2-1.5x0.6-0.8 um, are patternless, except for a vestigially developed axial thickening. Spine scales, (1.1) 1.9-2.3 (7.2) um long, consist of shaft, base-plate and lateral wings. Shaft narrow, non tubular, tapering to a blunt apex. Wings, ca. 0.08 um broad, to be found on either side of the shaft. They are broadest just beyond the base-plate but then narrow gradually towards the distal end of the shaft. Base-plate ca. 0.5 um in diameter, reniform or heart-shaped, surrounded by a narrow peripheral rim. (ref. ID; 4724)

Remarks

A. scaposa is remarkable in that two otherwise always separate characteristics are combined in its spine scales: lateral wings and heart-shaped base-plates. Variation with in A. scaposa is most noticeable with regard to the size of the spine scales. Whereas those from the majority of the Chilean habitats and from Sri Lanka vary from 1.9 to 2.3 um, those from a swamp near Puerto Montt/Chile are 7.2 um long. There is, however, no reason to believe that this difference should be considered anything but infraspecific variation. It may indicate the presence of different clones, or different stages in the cell or life cycle. (ref. ID; 4724)

Etymology

From the Latin scaposa, with shaft. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected on September 14, 1979 from the Banado Cruces, southern Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.1). (ref. ID; 4724)

Acanthocystis serrata Nicholls, 1983 (ref. ID; 7206 original paper)

See

Acanthocystis aculeata (ref. ID; 4710), Choanocystis aculeata (ref. ID; 4745)

Diagnosis

Cells 35-45 um in diameter (excluding scales) with scales of two types. Spine-scales 8-16 um long, slightly curved, hollow, 0.5-0.7 um wide and tapered slightly to a blunt apex with a saw-toothed margin of 5-10 triangular teeth. Proximal one-third of spine shaft ornate with lateral siliceous nodules and papillae up to 0.7 um long. Base of spine seated eccentrically on a nearly circular base plate (1.7-3 um in diameter) at the apex of a sinus or cleft in the base plate. Edges of the cleft rounded. Plate-scales patternless, 4-6 um long with swollen ends 2.2-3 um wide and a marked median constriction 0.7-1 um wide (dumbbell shape). (ref. ID; 7206)

Remarks

With the light microscope, A. serrata appears similar in size and outline to A. aculeata Penard. However, the siliceous papillae on the spines of A. serrata can be easily seen with the light microscope. The occurrence of these papillae is a constant feature in specimens from Ontario and have not been observed in any other species of the genus. If Penard (1904) and Rainer (1968) had this species under observation, they too should have been able to see the papillae since they were able to see and describe other structures such as plate-scales which are more difficult to resolve with the optical microscope, but are much different in shape from those of A. serrata. The dumbbell-shaped plate-scales of A. serrata appear in the light microscope like those of A. pelagica Ostenfeld; however, A. pelagica is a marine species which lacks papillae on the shaft of the sharp-pointed spines. The blunt apices of A. serrata's spines are obvious with the light microscope. (ref. ID; 7206)

Type material

Type from Calabogie Lake (45 degrees 16'N, 76 degrees 45'W), collected September 6, 1978 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0478), Ottawa. (ref. ID; 7206)

Acanthocystis spinifera Greeff, 1869 (ref. ID; 3541) reported year? (ref. ID; 1334), Greeff, 1869 emend. Penard (ref. ID; 3691) or Greeff, 1869 emend. Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper)

Emended diagnosis

Cell diameter 27-30 um. The spine-scales are 4.6-5.3 um long, not abundantly present and rather fine. They have a cylindrical shaft, which is irregularly bent and set on a circular basal plate, centrally or, mostly, slightly eccentrically. The shaft tapers slightly to the apex. The apex is about 0.07 um broad and bears two or three blunt teeth. The basal plate is 0.7 um in diameter. The plate-scales have distinctly concave sides; they are thin, flat and slightly ovoid, 3.4-4.4x1.7-2.6 um, with a small marginal rim; their surface is smooth. (ref. ID; 4745)

Comments

The only species which resembles A. spinifera is A. clavata. A. clavata, however, has a centrally seated shaft and a closed blunt apex. Its spine- and plate-scales are nearly half the size of those of A. clavata, while the basal plate of A. spinifera is nearly twice the diameter of the basal plate of A. clavata. (ref. ID; 4745)

Acanthocystis striata Nicholls, 1983 (ref. ID; 4710, 4725, 7206 original paper)

Diagnosis

Cells 7-10 um in diameter (fixed), with two kinds of scales. Spine-scales a hollow shaft, 3-7 um long, 0.12-0.2 um wide and tapered bluntly to a rounded apex. The proximal half of the spine shaft is bordered by an obovoid membrane with a periferally thickened margin about 0.02 um wide. The surface of the membrane is transversed with 20-42 radiating ribs (0.02 um wide) connecting the margin of the membrane with the proximal half of the spine shaft. The base of the spine shaft is bent, drawing the central area of the membrane into a depression and imparting a spoon- or ladle-shaped appearance to the spine-scale. Plate-scales elliptical (1.4x2.2 um) with a median tubular thickening approx. 0.07 um wide with tapered ends and two-thirds the length of the scale. Edge of the scale bordered by a broad fold or thickened margin ca. one-half the width of the scale and patterned with numerous radially disposed ribs 0.02 um wide. Similar ribs connect the median thickening to the scale margin. (ref. ID; 7206)

Descriptions

Only one isolated spine-scale was observed, with a shaft 2.50x0.15 um and a banded basal membrane 2.0x2.3 um, slightly more rounded than in the type. (ref. ID; 4710)

Remarks

The banded membranes of the spine-scales of A. striata are unlike those of any other known Acanthocystis species. In addition to the type locality, it was also found in Pond No. 3. (ref. ID; 7206)

Type locality

Type from Pond No. 1 (44 degrees 48'02"N, 78 degrees 29'W), collected May 5, 1981 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0479), Ottawa. (ref. ID; 7206)

Acanthocystis takahashii Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 20-30 um in diameter (measurement based on whole mount) with two types of scales. Plate scales, 2.5-3.2x1.5-1.8 um, elliptical or pear-shaped, patternless except for a narrow marginal rim and an axial thickening. Spine scales, 2.5-10 um long, tripartite, consisting of base-plate, shaft and trifurcate apex. Shaft, 0.19 um thick, cylindrical and hollow, attached to a circular base-plate, 0.5 to 0.8 um in diameter, surrounded by a narrow marginal rim. Apex separated into 3 diverging arms interconnected by a flaring of the distal portion of the spine shaft. Arms tapering, distal edges with 1-4 small teeth. Spine scales apically closed. (ref. ID; 4724)

Remarks

The appearance of A. takahashii is reminiscent of A. cornuta, but a confusion of the two is ruled out by the shape of the spine scale apices: trifurcate in A. takahashii, bifurcate in A. cornuta. In all other aspects the species are similar. EM-micrographs of single spine scales and broken periplasts belonging to A. takahashii have been published by Takahashi (1959) from Japan, as microplankton sp. No. 7 from Arasawa-dam. The fine structure of A. takahashii has been studied by Bardele (1977) but he, however, classified them with A. pectinata Penard (Bardele. pers. comm.). (ref. ID; 4724)

Etymology

In honour of Prof. Eiji Takahashi, Japan, who was the first to publish EM-micrographs of Acanthocystis scales. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected 6 March 1983 from a small pond near Batticaloa, E. Sri Lanka and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.11). (ref. ID; 4724)

Acanthocystis trifurca Nicholls, 1983 (ref. ID; 7206 original paper)

See

Acanthocystis myriospina (ref. ID; 4710)

Diagnosis

Cells (6-) 8-12 (-18) um in diameter with scales of two kinds. Spine-scales 2.5-10 um long and mostly straight or with some curvature near the base. Spines hollow, 0.15 um in diameter near the base and tapering to about 0.10 um distally. Tip of spines separated into three arms 0.08-0.25 um long, each usually tapered to a sharp point, but sometimes slightly bifurcate or swollen and rounded. Base of spine, a shallow inverted cup, 0.5-0.7 um in diameter usually with a thickened marginal rim. Plate-scales circular to elliptical, 1.0-2.4x1.3-3.6 um. Perifery of scales with a thickened rim 0.015-0.030 um wide. An axial fold or thickening is present in the middle of the scale and occupies up to two-thirds of the length of some scales but is much less developed or absent in others. (ref. ID; 7206)

Type locality

Type from Buckskin Lake (44 degrees 57'N, 78 degrees 11'W), collected May 3, 1977 and filed with the National Museum of Natural Sciences (No. NMCIC1983-0480), Ottawa. (ref. ID; 7206)

Acanthocystis tropica Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast 20-30 um in diameter (measurement based on whole mount); details of protoplast unknown. Scales of two types. Spine scales, 4-7 um long, consisting of shaft, lateral wings and basal wing. They are usually bent in the proximal half of their length. Shaft, 0.19 um in diameter, hollow, tapering abruptly to a pointed apex. The lateral wings are proximally rectangular but then narrow abruptly and taper distally along the shaft to terminate subapically. The outer corners thus formed are sometimes expanded. Cross ribs are developed, mainly on the proximal part of the lateral wings and on the basal wing. Plate scales, 2.1-2.7x1.2-1.5 um, elliptical, ornamented with distinct radial slits and a moderately elaborated axial thickening. (ref. ID; 4725)

Remarks

A. tropica bears some likeness to A. erinaceoides and A. pinnata, for instance in the spatulate appearance of the spine scales, the curved, tapering shafts, the triangular basal wing, as well as in the broad lateral wings which narrow abruptly. Distinguishing characteristics are the rib-pattern present on the wings and the ornamentation of the plate scales. These lack the central swelling, which is typical of A. erinaceoides and A. pinnata. In regard to the ribbed wings, A. tropica shows some relationship to A. pantopodeoides and A. fortesca and to some other species described in this paper: A. kilianii and A. tropica ssp. paucistriata. Because of the abruptly cut off shaft ends, A. pantopodeoides, A. fortesca and A. kilianii are considered to be closer to species of Group B than are A. tropica and A. tropica ssp. paucistriata. Despite all differences in the morphology of the spine scales, the rib pattern suggests that all species with this characteristic are more or less related. (ref. ID; 4725)

Etymology

From its occurrence in the tropics. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 7 March 1983 from Tissa Lake, southern Sri Lanka, and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.4). (ref. ID; 4725)

Acanthocystis tropica ssp. paucistriata Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Differs from A. tropica ssp. tropica in that the basal and lateral wings have distinctly fewer ribs and the plate scales completely lack radial slits. Periplast 15-25 um in diameter, spine scales 2.8-5.0 um long, plate scales 2.0-2.5x1.2-1.3 um. (ref. ID; 4725)

Remarks

The two distinctive features mentioned above are clearly visible on both subspecies. However, individuals spine scales of A. tropica ssp. paucistriata may appear almost free of cross ribs making a confusion with A. pinnata possible. This species is usually defined by the central swelling of the plate scales, but single scales have been observed where this structure is rudimentarily developed. This implies that especially these taxa cannot be identified from finds of single plate and spine scales alone and that whole periplasts are needed, for reliable identification. (ref. ID; 4725)

Etymology

From the Latin paucistriatus, with few striae. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 25 July 1981 from the Banado Rio Cruces, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.5). (ref. ID; 4725)

Acanthocystis tubata Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, ca. 25 um in diameter (measurement based on whole mount), with two types of siliceous scales. Details of protoplast unknown. Plate scales ovoid or elliptical, 2.9-3.7 um long and 2.2 um wide, patternless, except for an axial thickening. Spine scales, 6-11 um long and 0.23 um wide at the narrowest point. Shaft cylindrical, gradually expanding towards the distal end. Apex, 0.4 um in diameter, covered by a thin siliceous layer. A circle of about 12 conical teeth surrounds the apical margin. Base of the shaft supported by a circular, centrally depressed baseplate (diameter 1.2 um) with peripheral rim. (ref. ID; 4724)

Remarks

A. tubata species reveal in the light microscope a striking similarity to a A. mimetica Penard (1904), in the gradually expanded spine scale shafts, their circular base-plates and the dimensions of cells and scales. The only feature which contradicts an identification with A. mimetica is the absence of a conspicuous horseshoe-like rim reported by Penard from the surface of the plate scales. Such a "rim" appears sometimes during the LM observation of uneven structured plate scales, especially when these are somewhat tilted. Those scales are present, for instance in A. rotundata Nicholls ssp. rotoairense (this paper) and A. pantopodeoides Nicholls (syn. A. cuneiformis Durrschmidt). Thus it is assumed to be only an optical effect. However, the plate scales of A. tubata are flat. As no type material has been left by Penard, as inquiries at the following institutes revealed (British Museum, London; Museum D'Histoire Naturelle, Geneva; The Royal Microscopical Society, London; Museum National d'Histoire Naturelle, Paris) it will remain unclear on which specimens Penard based the diagnosis of A. mimetica. A. tubata is easily recognized under the electron microscope by the shape of the spine scales. No variation in scale structure has been observed in specimens from different localities. (ref. ID; 4724)

Etymology

From the Latin tubata, trumpet-like. (ref. ID; 4724)

Type slide

Type specimens found in a surface sample collected 11 July 1982 in a swamp near Maramaranui, North Island, New Zealand and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.3). (ref. ID; 4724)

Acanthocystis turfacea Carter, 1863 (ref. ID; 3541, 3691, 4687, 4710) reported year? (ref. ID; 7206) reported author and year? (ref. ID; 4009)

Synonym

Acanthocystis chaetophora Leidy, 1879 (ref. ID; 3541) reported year? (ref. ID; 3691); Acanthocystis pallida Greeff, 1869 (ref. ID; 3541) reported year? (ref. ID; 3691); Acanthocystis viridis Grenacher, 1869 (ref. ID; 3541) reported year? (ref. ID; 3691); Actinophrys viridis Ehrenberg (ref. ID; 3691)

Descriptions

Cells 10-150 um in diameter (in literature). Plate and spine scales are separately arranged in two close-set superposed layers. How the spine scales are fixed is not known. The plate scales, 3.7-4.2x1.9-2.2 um, are elongated ellipsoidal, often slightly curved to one side. Ventral and dorsal surface are smooth and patternless apart from a weakly developed central ridge. In SEM they appear flat or slightly convex. Spine scales are of 2 kinds: (i) one kind is long, 12-30 um, terminating distally into a short and flattened furcate apex; shaft tubular, not tapering. Proximal ends with round, flared, plate-like bases (base-plates), 1.4 to 1.5 um in diameter, which are narrow-rimmed and deeply convex towards their middle part. Spine scales of the second type (ii) differ in that they are shorter, 6-14.5 um their shafts more slender and provided with wide furcate apices. Variation within A. turfacea was most noticeable, with regard to the size of the scales and the length of the apical furca. (ref. ID; 4687)
A. turfacea is easily recognised by light microscopy and has been recorded worldwide. The cell observed from Lake Garcia was 20 um in diameter, with markedly bifurcate spine-scales 3.3-13.2 um long with a base 1.5-2.0 um in diameter, and weakly bifurcate spine-scales 10.6-21.2 um long with a base 2.2 um in diameter. Cells from Jock's Lagoon were 55-59 um in diameter, with spine-scales up to 50 um long. The oblong plate-scales of these cells measured 3.6 to 4.9x4.9-6.6 um. Several pores were observed in the layer of plate-scales, regularly spaced over the surface of the cell and measuring approximately 1.0 um cross. The pores presumably allow the passage of food and waste material through the plasma membrane, in the manner described for this organism by Nicholls (1983). (ref. ID; 4710)

Remarks

Carter (1863) first described A. turfacea, which he found in heath bogs on the southern Devon coast. He did not observe the shorter kind of spine scales nor the presence of plate scales. More detailed descriptions were then given by Greeff (1869), who identified the species as A. viridis (Ehrb.) Carter and, together with excellent drawings, by Leidy (1879) who classified it as A. chaetophora. A. turfacea is one of the few Acanthocystis species which can be identified with certainty by LM. Thus, only little can be added to the previous descriptions of the scale structure. However, it is possible to define A. turfacea more exactly. The periplasts illustrated from a whole mount in Figs. 1, 2, compare closely with those of Penard's collection. (ref. ID; 4687)
The large size of this species together with its investiture of forked spines which can be easily identified by light microscopy have undoubtedly contributed to world wide recognition of this taxon. Earlier studies with the light microscope divided the spine-scales into two groups: short ones with marked bifurcation of the apices and much longer ones with weak bifurcation. The electron microscope revealed a double bifurcation of all apices of short spines and tiny teeth of the bifurcate apices of the long spines. There are also usually present many spines intermediate length (25-35 um) which had a degree of bifurcation intermediate between that of the short (8-15 um) and that of the long (45-65 um) spines. Degree of bifurcation appears to be inversely related to spine length. The spines are hollow and are seated on a circular disc 2.3-4.5 um in diameter. The most important new finding concerning. A. turfacea's anatomy relates to the fine structure of plate-scales and spine-scales. The exterior of the plasm membrane is covered with a layer of overlapping oblong scales (3.5-5.5x8-12 um) lacking a marginal rim and any other ornamentation except a weakly developed axial thickening oriented longitudinally and occupying a central position on some scales. This structure is much better developed in other members of the genus. (ref. ID; 7206)

Acanthocystis umbraculiformis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast, 15-25 um in diameter (measurement based on whole mount) with two types of scales; details of protoplast unknown. Spine scales are umbrella-shaped, 2.4 um in diameter, with a short stalk, 0.6 um. Delicate radial ribs ornament the umbel and become blurred towards the centre. Plate scales, 1.5x0.8 um, are elliptical, sometimes slightly curved, smooth, with a poorly-developed axial thickening. (ref. ID; 4725)

Remarks

The spine scales of A. umbraculiformis are somewhat reminiscent of those of A. pulchra. However, a shaft is no longer detectable and the scales are radially symmetrical, which is also the case in A. flabellata. The finds of similar spine scales indicates that there are other closely related species. (ref. ID; 4725)

Etymology

From the Latin umbraculiformis, umbrella-shaped. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 14 September 1979 from the Banado Rio Cruces, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.2.8.1). (ref. ID; 4725)

Acanthocystis valdiviense Durrschmidt, 1987 (ref. ID; 4724 original paper)

Diagnosis

Periplast, 20-25 um in diameter (measurement based on whole mount), with 3 kinds of scales. Details of protoplast unknown. Plate scales, 1.2-1.8 x 1.0 to 1.5 um, elliptical or ovoid, periphery with a small thickened rim, and with an axial thickening poorly developed and sometimes asymmetrically placed in the centre. Otherwise they are thin and patternless. Spine scales of two kinds, all with tubular straight shafts (0.17 um in diameter), round base-plates (0.58 um in diameter) and apically always with 4 pointed teeth. The base-plate are centrally depressed and surrounded by a narrow marginal rim. One kind of the spine scale (S1) is 5-7 um long, with only slightly expanded distal ends and short distal teeth. The other (S2) is usually half as long (ca. 2.6 um) with distinctly expanded apices and longer apical teeth. (ref. ID; 4724)

Remarks

It is evident from EM micrographs that A. valdiviense is similar to A. polymorpha Durrschmidt and taxa of A. pectinata (Penard) Nicholls in regards to the shape of the spine scales. The most distinctive characteristics of A. valdiviense are (1) the fixation of the number of apical points of 4 (6-8 in A. pectinata ssp. and A. polymorpha), (2) the minor flaring of the distal portion of spine scale type (S2) (0.4-0.6 um compared to 1.1-1.5 um in A. pectinata ssp. and ca. 2.0 um in A. polymorpha), and (3) the length of the cylindrical portion of the shaft (2.2 um compared to 1.3 um in A. pectinata and 4-8 um in A. polymorpha). There are also differences in the appearance of the plate scales. These are conspiciously larger in the case of A. polymorpha and more electron dense, while in A. pectinata ssp. additional ornamentations such as slits and dots are developed. A. valdiviense bears also a certain resemblance to A. penardi ssp. pusilla, for instance in the shape of the spine scales. However, both taxa are distinguished by the presence of only one type of spine scales, by the varying number of apical teeth (4-7), the less expanded distal ends, and by the pyriform and dotted plate scales. The differences in scale structure outlined above justify the establishment of a separate taxon. However, more material, preferably from other countries and from clonal experiments, has to be analysed to see, whether a certain population of e.g. A. penardi or A. pectinata produces morphological variants, which, in the light of current knowledge are ascribed to different taxa. (ref. ID; 4724)

Etymology

From the type habitat near Valdivia. (ref. ID; 4724)

Type slide

Type specimens found in a water sample collected 8 September 1979 from a paludal forest (hualve) between Villarrica and Licanray, southern Chile and filed with the British Museum London, Protozoa Section (accession no. 1984.12.17.5). (ref. ID; 4724)

Acanthocystis veliformis Durrschmidt, 1987 (ref. ID; 4725 original paper)

Diagnosis

Periplast, 10-20 um in diameter (measurement based on whole mount) with two types of scales; details of protoplast unknown. The spine scales are reminiscent of a sail. The shaft is reduced to a short hollow rib. The lateral wings are continued along the whole length of the shaft reaching the maximum breadth in the lower 3rd of the scale. From here towards the proximal end they are closely anchylosed with the basal wing and form a short patternless stalk, sometimes only present as a concave depression around the proximal shaft end. The lateral wings are ornamented with thin, delicate ribs, which run transverselly or obliquely from the shaft to the outer margin. Ribs are also present on the front part but here they run inwards from the outer margin. Plate scales are small, 0.9-1.3x0.6-0.8 um, ovoid or, more rarely, elliptical. They are patternless except for an axial thickening which is slightly shifted to the smaller pole of the plate scale, and a narrow peripheral rim. As indicated by SEM micrograph they are not even by with distinctly concave middle parts, elevated submarginal parts and slightly inflexed margins. (ref. ID; 4725)

Remarks

The spine scales of A. veliformis suggest, because of the rudimentary stage of the stalk, recognizable only as concave depression, that they might present a basic type from which stalked spine scales may have been developed. Other closely related species are A. formosa Durrschmidt (1985) and A. ovata, whose spine scales may derived from those of A. veliformis by further reduction of size, shaft and rib pattern, though to a different degree. (ref. ID; 4725)

Etymology

From the Latin veliformis, sail-shaped. (ref. ID; 4725)

Type slide

Type specimens found in a water sample collected on 14 September 1979 from the Banado Rio Cruces, Chile and filed with the British Museum London, Protozoa Section (accession no. 1985.1.30.14). (ref. ID; 4725)

Acanthocystis wiasemskii Ostroumoff, 1917 (ref. ID; 3541, 7658 redescribed paper)

Emended diagnosis

Cells 25-30 um in diameter. Periplast comprising plate scales and one type of spicules. The spicules are of similar length, 12-15 um, nail-shaped; the shaft is straight, hollow, ca. 0.6 um, abruptly tapering to the sharp apex; the base-plate is circular, ca. 2.3 um in diameter. The plate scales are bean-shaped, patternless, 4.0-5.0x2.0-2.5 um. (ref. ID; 7658)

Remarks

This species was formerly described by LM observations only. Organisms studied by us are the only known marine heliozoa which are similar to those collected by Ostroumoff (1917). They differ from the diagnosis by shorter spicules and by the presence of plate scales in the periplast. However, radial parts of spicules with sharpening ends are quite similar to those in the Ostroumoff's figures. Only fresh-water A. clavata Durrschmidt, 1987 has nail-like spicules without any teeth at the apex, however its spicules are more thin and short, curved and possess blunt apices. Plate scales in organisms studied are bean-shaped and could taken erroneously for horseshoe-shaped base-plates in LM by Ostroumoff; their size and shape are more similar to those described for base-plates. In natural environments A. wiasemskii was collected in the Black Sea. (ref. ID; 7658)

Locality

The marine aquaria in the Institute for the Biology of Develpoment. (ref. ID; 7658)