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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Paulinella

Paulinella Lauterborn, 1895 (ref. ID; 3686, 3712, 5772), Lauterborn, 1895 emend. Hannah, Rogerson and Anderson, 1996 (ref. ID; 7360)

Amoebae: Filosea Leidy, 1879 [ICZN] (ref. ID; 5772)

[ref. ID; 1618]
Test small ovoid, not compressed; with siliceous scales in alternating transverse rows; aperture terminal; body does not fill the test completely; nucleus posterior; among vegetation in fresh or brackish water. (ref. ID; 1618)

[ref. ID; 1923]
Shell small, oviform. (ref. ID; 1923)

[ref. ID; 3626]
The genus Paulinella was established by Lauterborn in 1895 for the rhizopod with blue chromatophores that he described from the freshwater meander of the Rhine River. (ref. ID; 3626)

[ref. ID; 3686]
Shell colourless or yellow; ovoid and circular in transverse section; composed of elongate, curved siliceous shell-plates, aperture terminal oval with a small neck. (ref. ID; 3686)

[ref. ID; 5772]
Testate amoebae with internally formed siliceous scales. The scales are rectangular or elongate hexagonal plates, which are arranged in longitudinal columns (usually five) (Johnson et al. 1988; Lauterborn 1895). (ref. ID; 5772)

[ref. ID; 7360]
Testate amoebae surrounded by a wall of internally formed siliceous scales. Scales can be rectangular in shape or as elongate hexagonal plates, which are arranged in regular longitudinal columns or as staggered rows. (ref. ID; 7360)
Remarks; The genus Calycomonas was described by Lohmann in 1908 to include those small uniflagellate colourless monads enclosed in yellow envelops. Included in this genus were several forms of a single species, Calycomonas gracilis, which were later separated by Wulff (1916). One of the smaller, oval-shaped forms was given the name Calycomonas ovalis, however, more recent work by Johnson et al. (1988 see: ref. ID; 3626) has shown that this presumed chrysophyte was in fact a testacean rhizopod. They presented electron microscopic evidence showing that the thecal siliceous scales were morphologically and ultrastructurally similar to those laid down by Paulinella chromatophora Lauterborn 1895. This, together with the observation that cells fed on bacteria using a filose pseudopodium, resulted in a redescription of the organism as P. ovalis (Johnson et al. 1988). The type species, P. chromatophora, has only been found in freshwater or brackish habitats (Geitler 1927; Kepner 1905; Kies 1974; Lackey 1936; Pankow 1982). However, P. ovalis became the first member of the genus, and indeed the first testate rhizopod, to be isolated from a full salinity, estuarine environment (Johnson et al. 1988). Since then another marine species of Paulinella has been described. Vors (1993) described P. intermedia from a seawater sample collected off the coast of Tenerife, Canary islands. It is now generally accepted that the genus is ubiquitous in the marine environment having been found in the Baltic, North Sea, Barents Sea, Coastal Norway, Eastern North America, New Zealand and Japan. All three described Paulinella species are oval in outline with scales covering the test. These are rectangular, curved and rounded at the edges and are deposited in columns along the longitudinal axis of the test. In P. ovalis, there are 5-6 scales per column, in P. chromatophora the largest species described, there are 9-12 scales per column (Johnson et al. 1988; Kies 1974; Lackey 1936; Lauterborn 1895) while in P. intermedia there are 6-7 scales per column (Vors 1993). In all cases, the aperture was surrounded by three or four neck plates. In two of the three described species, filose pseudopodia have been observed; the description of P. intermedia was based solely on a shadow-cast whole mount preparation of a single test (Vors 1993). (ref. ID; 7360)
Type species; Paulinella chromatophora Lauterborn, 1895 (ref. ID; 7360)
  1. Paulinella chromatophora Lauterborn, 1895 (ref. ID; 3626, 3712, 4823, 7360) reported year? (ref. ID; 1618, 1923, 3693, 5703, 6792)
  2. Paulinella indentata Hannah, Rogerson and Anderson, 1996 (ref. ID; 7360 original paper)
  3. Paulinella intermedia Vors, 1993 (ref. ID; 5772 original paper, 7360)
  4. Paulinella ovalis Johnson, Hargraves & Sieburth, 1988 (ref. ID; 3626 redescribed paper, 7360)
  5. Paulinella ovalis (Wulff, 1916) (ref. ID; 7360)

Paulinella chromatophora Lauterborn, 1895 (ref. ID; 3626, 3712, 4823, 7360) reported year? (ref. ID; 1618, 1923, 3693, 5703, 6792)

Descriptions

Scales arranged in eleven to twelve rows; with one to two curved algal symbionts; no food particles; a single contractile vacuole. (ref. ID; 1618)
Shell colorless or of a pale lemon color, not compressed, with a small oval aperture provided with a short neck; scales arranged in alternating transverse rows. Protoplasm devoid of food particles, with 2 sausage-shaped curved symbiotic blue-green algae. These Cyanelles are minute Cyanophceae, having the same function as the zoochlorellae (Chlorophyceae). Habitat submerged vegetation. (ref. ID; 1923)
Paulinella chromatophora is large enough (up to 35 um long) to be adequately diagnosed by light microscopy as a filose amoeba living within a test. The internally formed siliceous scales are rectangular and arranged in columns parallel to the long axis of the test and pseudostome, unlike the alternating oval scales of Euglypha, and were the reason de Saedeleer established a new family, Paulinellidae, separate from the Euglyphidae and Cyphoderiidae. Paulinella chromatophora is also distinguished by having one or two short filaments of an endosymbiotic cyanobacterium which give it the noticeable blue color. These symbionts (or cyanelles) through their photosynthesis, make a significant contribution to the metabolism of this testacean, so much in fact, that it has been suggested that P. chromatophora does not ingest particulate food since it lacks digestive vacuoles. (ref. ID; 3626)
Shell elliptical, sackshaped (ca. 10x20 um), circular in transverse section. Collar short (3 um) but prominent. The shell is composed of homogenous, transparent, six-sided elongated scales, arranged circumferentially in columns of about 8 plates. The cytoplasmic body almost completely fills the shell. The maximum length of slender pseudopodida reaches half of the shell length. Nucleus elliptical (ca. 5x8 um) with a reticular structure situated in the posterior part of the body. One nucleolus is clearly distinguishable in the nucleus. One vacuole is situated in the anterior part. Two to six cyanelles 3-4x16-18 um, sausage-shaped, of blue-green colour with pale central part. Cyanelles divide into two parts of similar size by invagination of cell wall, upright to longitudinal axis. (ref. ID; 4823)
Molecular evolutionary analyses of nuclear-encoded small subunit ribosomal RNA (Strain collected by I. Reize in 1990 from a pond in Aussenstelle Lochmuhle near the Forschungsinstitut Senckenberg in Bierbergemund-Bieber, Germany). (ref. ID; 5703)

Comments

Paulinella chromatophora was originally described by Lauterborn (1895) from stagnant water of the river Rhine. (ref. ID; 4823)

Measurements

20-32 um long; 14-23 um in diameter. (ref. ID; 1618)
Length 20-32 um. (ref. ID; 1923)

Paulinella indentata Hannah, Rogerson and Anderson, 1996 (ref. ID; 7360 original paper)

Diagnosis

Cells oval in outline ranging from 11.7 to 17.0 um in length by 8.3 to 10.6 um in width. The aperture is elliptical, bounded by two to four collar plates; internal maximum dimension of opening 2.8-5.0 um. The test is covered in scales (approximately 6.0x3.0 um) arranged in staggered rows. Individual scales rectangular with rounded corners and a groove running centrally down their length. Two internal channels run through each adjacent raised area and the external surface contains rows of pores. When active, numerous filose pseudopodia, sometimes branched, extend up to 50 um from the cell aperture. (ref. ID; 7360)

Descriptions

Light microscopy: Tests are oval in lateral outline with a short collar. Under phase contrast, evidence of attached scales is seen. In culture, the cytoplasm of the cells appears to fill the test which is pale yellow in colour. No ovivous cytoplasmic inclusions were noted and nuclear measurement were not made prior to the loss of cultured material. Active cells commonly have numerous filose pseudopodia extending from the aperture. There are occasionally branched and can extend up to 50 um from the test opening. The average length of test of strain KB is 15.8 um (S.D. 1.3; range 11.7-17.0) and the mean width is 9.8 um (S.D. 0.7; range 8.3-10.6). Apertures are oval in outline and have a mean mximum dimension of 3.9 um (S.D. 0.6; range 2.8-5.0). The number of aperture plates forming the collar varies between two and four. The test of strain KB is covered with approximately 22 scales, mean length 5.7 um (S.D. 0.4; range 5.3-6.2) by mean width 2.9 um (S.D. 0.1; range 2.8-3.1). Scales are arranged on the test in staggered rows, as opposed to columns in the case of other species. Individual body scales are rectangular with rounded corners. Scales are curved and markedly indented along their median axis. In cross sections of broken shells, or in the case of inadequately formed scales, it is clear that the raised areas on either side of the depression are hollow. The thickness of scales is proximately 0.2 um in the deression and about 0.6 um in the raised portion. The posterior of the cell is covered in smaller scales of slightly different morphology. Here, the indentation is more pronounced. Individual scales are punctuated with rows of pores, approximately 0.07 um diameter, that run around the periphery of the scale and along the edges of the depressions. Usually the ends of the scales have three or four rows of pores but only a single row along their length. In dividing cells, which attach at their apertures, the plates on the parent wall show more detail than the developing scales on the daughter cell. Presumably, this is due to the presence of an organic layer on the outside of the newly deposited plates. The posterior of the newly found cell is devoid of scales. Instead it appears to consist of a cytoplasmic extrusion, or perhaps a naked, organic wall normaly underlying scales. The lack of scales in this region gives information about the deposition sequence and suggests that plates are externalized and deposited last in the posterior region to the test. (ref. ID; 7360)

Remarks

The morphology and size of the scales in strain KB are quite distinctive. Individual scales are around 5.5 um in length with a pronounced central depression. This is particularly evident in scales located at the posterior of the test. Moreorver, scales had two hollow channels running through the plates below each of the ridges and the surfaces are punctated by rows of pores. P. chromatophora has similarly sized plates (around 6.5-um long) with several porous sieve plates on the edge of scale (Kies 1974), but, the rectangular plates are without ridges or depressions. The scales of P. intermedia are also curved and smooth in cross section (Vors 1993) but in this species they are considerably smaller (around 1.7-um long). The only species to have ridged scales with an external fine pored surface is P. ovalis but here only one ridge runs along the centre of the scale (Johnson et al. 1988). The scales are distinctly hollow and much smaller (around 1.5-um long) than those in the present isolate. Strain KB was also unusual in that it is the only species to have scales arranged in staggered rows rather than in regular columns. All species of Paulinella had characteristically oval tests with apertures surrounded by collar plates. However, the dimension of the test of strain KB (mean length 16 um) was only close to that of P. chromatophora which has a test in the range 17 to 35 um, depending on geographic location (Bovee 1985). Both P. ovalis and P. intermedia are smaller with test lengths of approximately 4.5 um and 6.6 um, respectively. We conclude, therefore, that the KB isolate is a new species within the genus Paulinella and name it Paulinella indentata n. sp. (ref. ID; 7360)

Etymology

The specific name comes from the characteristic indented pattern on the test scales. (ref. ID; 7360)

Type locality

Subtidal sand (8 m depth), Kames Bay, Isle of Cumbrae, Scotland. Salinity 32.9 0/00. (ref. ID; 7360)

Deposition of types

Holotype material in the form of an SEM specimen prepared from the original clonal culture has been deposited with the Natural History Museum, London with the accession number 1995:9:18:1. (ref. ID; 7360)

Paulinella intermedia Vors, 1993 (ref. ID; 5772 original paper, 7360)

Diagnosis

Entire test composed of flat, rectangular plate scales with rounded corners. (ref. ID; 5772)

Descriptions

Only the test has been observed. The test consists of an ovate chamber with an apical short neck, and is composed of scales. The scales are flat, slightly bent, rectangular plates with rounded corners. The scales are arranged in columns parallel to the long axis of the test. There are 3-4 columns and 6-7 scales in each column. A few smaller scales are found at the posterior end of the test. The neck of the test is composed of three scales, which are narrower than those of the test chamber. (ref. ID; 5772)

Remarks

The test of Paulinella ovalis (Wulff) Johnson et al. (1988) is composed of five columns of 5-6 thick, curved and ridged scales. There are few thick scales at the posterior end, and three flat neck-scales. The average size of the test is 3x4.5 um, with a neck diameter of ca. 1 um. Newly formed scales are also thick and curved (Johnson et al. 1988). Paulinella intermedia is similar to P. ovalis in size, and in the number of scales composing the test, but it is distinguished by possessing flat scales only. Paulinella intermedia is too small to be referred to Paulinella chromatophora Lauterborn, 1895 which measures 12-22(-35) um in length and 15-20 um in width, with a neck diameter of ca. 5 um. The test comprises 5-6 columns of 9-12 scales (Johnson et al. 1988; Kies 1974; Lauterborn 1895). (ref. ID; 5772)

Type specimens

Collected at Callao Salvaje, Adeje, Tenerife. (ref. ID; 5772)

Measurements

Size of test: ca. 2.9x6.6 um, neck diam. ca. 1.9 um. (ref. ID; 5772)

Paulinella ovalis Johnson, Hargraves & Sieburth, 1988 (ref. ID; 3626 redescribed paper, 7360)

Redescriptions

Test 3.0x4.5 um, ovoid, clear to pale yellow, composed of internally formed Si scales that may become further mineralized with Fe and Mn. Scales arranged in five transversely circumferential columns parallel to the long axis; 5-6 curved rectangular scales with external central ridge per column; cross-section round. Pseudostome, terminal round, 1.0 um diameter, composed of three flat-sided, non-dentate, curved-rectangular scales. Pseudopod, filose, extending up to 25 um. Motility, a tumbling or rolling movement. Bacterivore (unicellular cyanobacteria). Symbionts absent. Forms new test at division as in Euglypha. Estuarine, planktonic habitat. The general shape of the test is oval in lateral views and circular in transverse views. The arrangement of scale plates produces the annular thickenings of the test wall observable by light microscopy. These curved-rectanguloid scales are arranged in columns, parallel to the long axis of the test, with five columns encompassing the circumference of the cell. There are five to six scales in each column. The ridged body scales differ visibly from the three, flat-sided oral scales forming the pseudostome. The posterior end of the test is covered by a few smaller body scales. This arrangement reveals a test composed of a total some 35 scales. The eukaryotic protoplast within the test had neither chloroplasts nor flagella. Phagotrophy was clearly evident by the frequent observation of unicellular cyanobacteria within some food vacuoles and digested cell contents in others. Paulinella ovalis captures its prey with an extremely fine pseudopod or filopodium extended through an opening in a membranous operculum. This pseudopodium, although generally difficult to observe by light microscopy, was best resolved using negative phase contrast. The anterior region of the protoplast was highly vacuolated with microtubules extending into the pseudopod. The pseudopod apparently also functions in motility giving a slow, tumbling/rolling movement to the test. The scales of P. ovalis are produced internally, transported through the cell, and arranged into an identical daughter test by the pseudopod. Scale production occurs adjacent to the Golgi in the silica deposition vesicle and its associated group of microtubules. Newly formed scales are hollow and have a fine pattern of pores to the ridged side of the very delicate electron-dense wall structure. The scales retain the fine pores after their release from the protoplast. Test formation involves a new organic matrix cementing or joining the new scales together. Observations of dividing cells by light microscopy show that a new test is more transparent and then progresses to equal the refractility and color of the parent test. (ref. ID; 3626)

Comments

The cellular organization and mode of division of P. ovalis is very similar to other members of the suborder Euglyphina which produce siliceous scales intrinsicallly such as Euglypha rotunda, Tracheleuglypha dentata, Trinema linear, and P. chromatophora. In these testaceans, the anterior region of the cytoplasm is highly vacuolated with reserve scale, pigment granule, and contractile vacuoles while the posterior region contains the nucleus, mitochondria, endoplasmic reticulum (ER), and Golgi apparatus. The siliceous scales are formed by a silicon deposition vesicle (SDV) bound by the silicalemma and derived from either the dense ER or the Golgi. The exception of P. chromatophora and P. ovalis, all the members of this suborder thus far described have reported from either freshwater, mosses, soil, or sewage. Scale production in P. ovalis is almost identical to that in P. chromatophora with the location of the silicon deposition vesicle (SDV) in the aboral region and its association with the Golgi. While the siliceous scales of most euglyphids appear to be solid and without internal structure, P. chromatophora scales have a discontinuous silicon interior and several porous "sieve-plates" on the side the scale facing the cytoplasm. Paulinella ovalis scales, however, are distinctly hollow in cross-section and composed of a delicate silicon framework with fine-pored external surface. The microtubules adjacent to the SDV, in both species of Paulinella, may be involved in the shaping of this vesicle and therefore its scales. Lochmann's original description showed three different test shaped and sizes for the organism he named Calycomonas gracilis. Further differentiation among these forms was made with the establishment of P. ovalis (C. ovalis Wulff and C. wulffii Conrad & Kufferath and with the type species being retained as C. gracilis Lohmann. While the species of Calycomonas are consistently referred to as "flagellated chrysophytes" or "phytoflagellates", clearly P. ovalis is not among this group. On the other hand, our observations of C. wulffii indicate that it is uniflagellate and its test differs from that of P. ovalis. Moreover, C. gracilis appears to have a flagellum as well, and the test structure is also unlike that of P. ovalis. The validity of Lund's other Calycomonas species and the problem of whether C. wulffii and C. gracilis are chrysophytes are still open questions and warrant further investigation. Our observations are evidence that P. ovalis, as redescribed here, is truly a member of the genus Paulinella and we thus remove it from the genus Calycomonas. The species name is retained as P. ovalis to be consistent with the original description of Wulff and since it aptly describes the shape of the organism. (ref. ID; 3626)