Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Hemigastrostyla

Hemigastrostyla Song & Wilbert, 1997 (ref. ID; 4905 original paper)

[ref. ID; 4905]
Diagnosis; Marine or brackish water Oxytrichidae with slightly cephalized body shape; mostly 8-10 frontal, 5 ventral and a few extra lateroventral cirri which possibly derive from the 6th (right-most) FVT-cirral anlage during morphogenesis; caudal cirri present. (ref. ID; 4905)
Comparison; This new genus differs from all other members within the family Oxytrichidae by 1) the cephalized cell shape, 2) the presence of a few extra, posteriorly positioned lateroventral cirri to the right of transverse ones and 3) (very likely) having 6 cirral anlage. (ref. ID; 4905)
Type species; Hemigastrostyla stenocephala (Borror, 1963) n. comb. (ref. ID; 4905)

  1. Hemigastrostyla enigmatica (Dragesco & Dragesco-Kerneis, 1986) Song & Wilbert, 1997 (ref. ID; 4905 redescribed paper)
    Syn; Oxytricha enigmatica Dragesco & Dragesco-Kerneis, 1986 (ref. ID; 4905)
  2. Hemigastrostyla stenocephala (Borror, 1963) Song & Wilbert, 1997 (ref. ID; 4905)
    Syn; Oxytricha stenocephala (ref. ID; 4905)

Hemigastrostyla enigmatica (Dragesco & Dragesco-Kerneis, 1986) Song & Wilbert, 1997 (ref. ID; 4905 redescribed paper)

Synonym

Oxytricha enigmatica Dragesco & Dragesco-Kerneis, 1986 (ref. ID; 4905)

Redescription

Cell shape elongate with both ends widely rounded, frontal portion more or less head-like; left margin only slightly convex while portion posterior to distal end of adoral zone of membranelles on right evidently convex. When viewed ventrally, one inconspicuous indentation (marginal groove) formed by right marginal row at about anterior 2/5 of cell length. Dorsoventrally significantly flattened (about 1:3-4). Dorsal side uneven, with central part thicker than posterior and anterior ends, right and left often forming a projection-like border. Pellicle, cortical granules very fine (<1 um), generally grouped rosettes-like and close to cilia. At high magnification (1250x), always numerous small (ca. 2 um in size) vacuole-like, ellipsoid globules at deeper level (beneath cortical granules) recognizable. Cytoplasm hyaline and colourless; cells frequently with many lipid droplets, 5-8 um across. Food vacuoles rarely to recognize, contain mostly flagellates and diatoms. Contractile vacuole not observed. Constant two large macronuclear nodules ellipsoid, located in about mid-body and left to cell margin, containing many spherical nucleoli; replication band often visible in non-dividing individuals. Micronuclei several to "many", small and near macronuclei. Movement slow to moderate crawling on bottom of petri dish. Sometimes more or less thigmotactic, adhering with the aid of transverse cirri on substrate. By swimming slowly rotating around its longitudinal axis. Characteristically 2-3 (usually 2) right marginal cirri arising from border and slowly waving up and down, while all other ciliary organelles stationary. Oral area narrow, posterior portion of adoral zone of membranelles (AZM) always half covered by cytoplasmic lip on right margin of buccal field. AZM about half of cell length with distal end of zone extending back far onto right side. Paroral and endoral membranelles slightly curved, almost parallel to each other. Three evidently enlarged cirri in anterior cell portion: 2 frontal cirri at most apical area of cell, one buccal cirrus (BC) at about middle way of frontal region, other 5 frontal cirri grouped always together, near distal end of adoral zone. Ventral cirri (VC) in two groups as in many other oxytrichids: 3 anterior VC located anterior to cytostome level and close to frontal cirri; 2 posterior VC near to transverse ones (TC). Except those 5 normal ventral cirri, always 2 extra lateroventral cirri (LVC, called "fimbriate caudal cirri" by Borror) right to transverse cirri and posterior end of right marginal row. Transverse cirri strong, about 20 um long, subterminally located. Marginal rows extending slightly spirally from upper-right to lower-left. Right row shortened anteriorly with its posterior end extending near to right one of transverse cirri. Left row turning onto dorsal side (at least on margin of cell) and almost confluent with caudal cirri posteriorly. All marginal cirri densely spaced, laying "firmly" on cell surface along marginal grooves. Bases of all cirri associated with well impregnated fibres. Constant 5 dorsal kineties (DK), DK1 shortened posteriorly while DK4 extending anteriorly only about halfway of cell. Except those 5 rows, one ciliary fragment anterior to right marginal cirral row consisting of several basal bodies. Dorsal cilia about 3 um long, very characteristically located within cup-shaped depression. (ref. ID; 4905)

Remarks

Two individuals in stages of physiological reorganization have been observed. Both of them seemed to possess 6 cirral anlagen instead of 5 as in most of other oxytrichids. If this estimation is confirmed, then the two lateroventral cirri should be derived from the posterior part of the right-most (6th) anlage. This might, thus, indicate a unique systematic position of this genus within the family Oxytrichidae. This rather peculiar species was originally reported as Oxytricha enigmatica from a brackish water pond in Benin, Africa (Dragesco & Dragesco-Kerneis 1986). According to their illustrations and description, it differs from the population studied here only in the number of the frontoventral cirri (13-14 vs. 13; not included the 2 extra lateroventral one), which might vary slightly ("8 ou 10 cirres frontaux, 4 a 5 cirres ventraux"). Additionally, it is stated to have 5-7 fine caudal cirri after staining (protargol impregnation?!). Since the base of ciliature (also the dorsal kineties) of this species is strongly argentophilic, those "caudal cirri" could be due to a misinterpretation (? form variation?), hence, we identify it with our organism. Hemigastrostyla stenocephala (Borror, 1963) n. comb. (formerly Oxytricha stenocephala) must be a very similar species found in Florida (Borror 1963, 1968). Compared with it, the Qingdao population differs in vivo in the less elongated body shape and the relatively shorter buccal field (40-50% vs. 25-30% of cell length). Borror did not give the exact number of frontoventral cirri, according to the illustrations, it should be about 15-16 (13 in Qingdao population) in total. Another difference is the length of dorsal cilia: in H. stenocephala the cilia are ca. 16 um, whereas in our form they are only about 3 um. So the separation of the both species is quite clear. (ref. ID; 4905)