Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Onychodromopsis

Onychodromopsis Stokes, 1887 (ref. ID; 2129, 4894)

Family Oxytrichidae Ehrenberg, 1838: Subfamily Oxytrichinae Jankowski, 1979 (ref. ID; 4894)

[ref. ID; 2129]
Flexible Oxytrichidae with 18 frontal, ventral and transverse cirri; caudal cirri present. Undulating membranes side by side. Several right and left marginal cirral rows developing from at least two anlagen in a single right and left row each; parental rows completely resorbed during morphogenesis. (ref. ID; 2129)
Note; Onychodromopsis resembles Pleurotricha Stein, 1859. However, it is distinguished from Onychodromopsis by the lack of caudal cirri, the rigidity of the body and the separation of the transverse cirri into two distinct groups. Thus, Foissner et al do not follow Butschli (1889), Borror (1972) and others, who synonymized Onychodromopsis with Pleurotricha. (ref. ID; 2129)

[ref. ID; 4894]
Improved diagnosis; Adoral zone of membranelles formed like a question mark. Undulating membranes rather straight and arranged side by side or in Oxytricha pattern. Frontoventral cirri in V-shaped pattern. Postoral ventral cirri in dense cluster underneath buccal vertex. Two pretransverse ventral and five transverse cirri. Two or more right and one or more left rows of marginal cirri. Caudal cirri present. Primordia V and VI of the proter originate from cirrus V/4 and V/3, respectively. No parental marginal rows retained after division. Dorsal morphogenesis in Oxytricha pattern. (ref. ID; 4894)
Remarks; Onchyodromopsis has been rather differently classified, e.g. as incertae sedis in the Sporadotrichina (Corliss 1979), in the Holostichidae (Tuffrau 1987), in the Amphisiellidae (Small & Lynn 1985; Tuffrau & Fleury 1994), or as synonym of Pleurotricha (Borror, 1972), which has, however, a rigid body and lacks caudal cirri. The reinvestigation of the type species revealed that Onychodromopsis is very likely the sister group of Oxytricha (Petz & Foissner 1996). Onychodromopsis flexilis has undulating membranes arranged almost in parallel, indicating that a Stylonychia-like pattern evolved also in the Oxytrichinae. However, other Onychodromopsis species have the plesiomorphic Oxytricha pattern. Onychodromopsis is easily confused with Paraurostyla, because of the increased number of cirral rows (Foissner et al. 1991). (ref. ID; 4894)
Type species (by monotypy); Onychodromopsis flexilis Stokes, 1887 (ref. ID; 4894)
  1. Onychodromopsis flexilis Stokes, 1887 (ref. ID; 1621, 2129 redescribed paper, 4894) reported year? (ref. ID; 1618)
  2. Onychodromopsis grandis Stein, 1859 (ref. ID; 1621)
  3. Onychodromopsis kahli Sramek-Husek, 1957 (ref. ID; 2129)
  4. Onychodromopsis tihanyiensis Gellert & Tamas, 1958 (ref. ID; 2129), tihanyensis Gellert & Tamas, 1958 (ref. ID; 4253)

Onychodromopsis flexilis Stokes, 1887 (ref. ID; 1621, 2129 redescribed paper, 4894) reported year? (ref. ID; 1618)

Descriptions

Standing pond water. (ref. ID; 1618)

Redescription

Body very flexible, broadly elliptical and dorsoventrally flattened up to 2:1. Macronuclear nodules ellipsoidal; nucleoli spherical to ellipsoidal, 1-4 um across in protargol slides. Micronuclei almost globular, usually one each in variable position in indentation of macronuclear nodules. Contractile vacuole with two collecting canals in mid-body near left margin. Cortical granules 0.8-1 um across, arranged in rather narrowly spaced rows underneath entire cell surface as in Oxytricha granulifera Foissner & Adam, 1983, colourless and rather compact, stain blue but become not extruded when methyl green-pyronin is added, impregnate faintly to intensely with protargol depending on method and bleaching time. A second type of granules, minute (< /_0.2 um) and invisible in live specimens, occurs in great numbers between the larger granules and stains red with methyl green-pyronin; when the stain is added, many of them become extruded and adhere to cirri and adoral membranelles. Cytoplasm colourless, in field population with many avour 1-4 um sized lipid droplets and 3-5 um long, colourless crystals mainly in posterior portion. Food vacuoles 15-20 um across, often contain Colpoda steinii and Polytoma sp.; in cultures feeding also on Cyclidium glaucoma, starch and up to 45 um long, slender bacteria carried over from raw culture. Glides moderately fast. All cirri of field population about 13 um long in vivo, insert in shallow cortical pits. Cirral composition only slightly variable, i.e. one basal body row more or less may occur in most FVT-cirri; first cirrus of inner left marginal row usually composed of three kineties. Transverse cirri only slightly projecting beyond posterior body margin. Marginal cirral rows open at posterior end, gap occupied by caudal cirri. Usually two left and two right marginal rows; left outer row, however, frequently much less conspicuous than right inner row because consisting on average of five cirri only, in 19% of specimens even lacking, one cell with short third row. Rarely, a very short third right marginal row is present, namely 1-7 cirri left of inner row (6%) or 2-3 cirri between inner and outer row (8%); very like, these remnants from last generation and/or young postdividers with parental cirri still in resorption. Dorsal cilia 3-5 um long, insert in shallow cortical pits, arranged in six kineties; kineties 1-3 almost as long as body, kinety 4 curved and commencing subequatorially, kinety 5 extends from anterior to mid-body, kinety 6 consists of 4-5 bristles only; frequently, some irregularly arranged cilia between kineties 3 and 4, very likely remnants from last generation. Three (4-5 in six out of 34 specimens) caudal cirri attached to dorsal kineties 1, 2 and 4, inconspicuous because not elongated and composed of four, rarely six cilia only. Adoral zone of membranelles conspicuous, about 40% of body length, distal portion ventrally covered by frontal scutum, cilia gradually shortened from distal to proximal end of zone; widest bases about 10 um in vivo. Buccal cavity occupying about one third of cell width, anteriorly slightly curved and merging into frontal scutum, posteriorly gradually deepened and covered by buccal lip. Buccal lip hyaline, bent upright to and continuous with frontal cell surface, commences at level of buccal cirrus, gradually widened posteriorly to form wedge-shaped structure obliquely merging into posterior buccal vertex; longitudinally bipartite by deep cleft containing proximal two thirds of paroral membrane, right sheet narrower than left. Paroral membrane anteriorly slightly curved, cilia about 8 um long. Endoral membrane straight inserts on right wall of buccal cavity, not recognizable in scanning electron micrographs because underneath buccal lip. Paroral and endoral usually side by side in silvered specimens, posterior portions rarely slightly intersecting in surface view of cell, both very likely composed of dikinetids. Pharyngeal fibres 30-55 um long in protargol slides, originate from adoral membranelles and paroral and endoral membrane. (ref. ID; 2129)
  • Cyst: Resting cysts globular to slightly ellipsoidal. Cyst wall colourless, about 2 um thick, compact; surface studded with about 2 um long, hyaline spines and sometimes separated by narrow, transparent layer from compact part of wall. Cyst contents (cell) usually conspicuously lobed, does not occupy entire cyst volume; however, when cyst is slightly pressed, its content expand, completely filling interior. Cortex distinctly striated. Cytoplasm contains many 1-3 um sized, colourless globules. Macronuclear nodules and micronuclei do not fuse. (ref. ID; 2129)

    Occurrence and ecology

    O. flexilis was found at two sites of the Prince Edward Islands, viz. in a slightly saline and acidic (pH 6.1) grass sward on rock at the seaward limit of vegetation on Marion Island and in a slightly saline and acidic (pH 6.3) moss sample collected between Poa and Callitricha vegetation near a penguin rookery on Prince Edward Island. (ref. ID; 2129)

    Measurements

    90-125 um long. (ref. ID; 1618)
    Specimens in pure culture on average 24% larger than in raw culture (mean length 112.8 um, SD 7.8, CV 6.9, extremes 98, 127 um; mean width 55.4 um, SD 6.0, CV 10.8 extremes 41, 70 um; n=30). (ref. ID; 2129)

    Onychodromopsis kahli Sramek-Husek, 1957 (ref. ID; 2129)

    Descriptions

    Description of this species is obviously based upon his own and Kahl's (1932) incomplete observations of O. flexilis and thus cannot be recognized as distinct species. (ref. ID; 2129)

    Onychodromopsis tihanyiensis Gellert & Tamas, 1958 (ref. ID; 2129), tihanyensis Gellert & Tamas, 1958 (ref. ID; 4253)

    Descriptions

    This species has two obliquely arranged ventral rows indicating that it belongs to another genus. (ref. ID; 2129)