Pseudokahliella marina, (Foissner et al., 1982) (Foissner, 1982)

Song, Xiaozhong Hu Weibo, 2003, Redescription of the morphology and divisional morphogenesis of the marine hypotrich Pseudokahliella marina (Foissner et al., 1982) from scallop-culture water of North China, Journal of Natural History 37 (17), pp. 2033-2043 : 2034-2041

Results

Morphological redescription (figures 1–11, 26–32; table 1)

Size in vivo about 120–175 × 50–75 µ m. Body shape constant, elliptical with both ends rounded, left side nearly straight or slightly concave and right side always convex (figures 1, 26, 27). Dorso-ventrally flattened about 3:1 (figure 2). Oral field conspicuous and large, about one-third of body width with a roof-like structure covering the posterior part of the adoral zone of membranelles (AZM), which is half to three-fifths of cell length (figures 1; 4, 27, arrowhead). Pellicle thick, but slightly flexible; cortical granules (extrusomes) conspicuous (c.1.0 µ m across), colourless, aligned along longitudinal axis of the cell (figure 6); when ejected, spindle in shape, about 5–7 µ m long (figures 5, 28). Contractile vacuole is not observed in vivo.

Cilia in adoral zone of membranelles (AZM) c. 20 µ m long. Frontal cirri strong, about 15–18 µ m in length, and other cirri comparatively fine, c. 10–12 µ m long. Dorsal bristles closely set, about 5–6 µ m long.

Endoplasm usually dark greyish, with numerous reflective and granular inclusions, especially in posterior half, giving the cell an opaque appearance at low magnification; several large food vacuoles easily recognizable in natural condition, containing bacteria, diatoms and other ciliates (figure 3). Macronuclear nodules oval to ellipsoidal, c.12 × 9 µ m after impregnation, distributed in C-shaped pattern; 4–8 micronuclei, about 1.5 µ m across, often adjacent to macronuclei (figures 8, (arrowheads), 10).

Movement moderately rapid, usually creeping on bottom of culture dish or sometimes swimming spirally around the long axis of cell.

Infraciliature as shown in figures 7–11, 29–32. AZM composed of 43–68 membranelles in the first population, 32–83 in the second population; undulating membrane (UM) conspicuously long, uniquely composed of one double-rowed structure, with densely arranged basal bodies (figures 7, inset; 31, 32, arrow). Constantly three enlarged frontal cirri (figure 32, arrowheads); usually seven to ten fronto-ventral rows plus one left and one right marginal row, of which the anterior parts of right marginal and one or two rightmost cirral rows run onto dorsal side. Among individuals examined (n> 50, including at the morphogenetic stages), at least five had two left marginal rows or one plus a short row (figures 9, 11, arrows; 30, arrow). Three complete dorsal kineties with densely arranged cilia. Without caudal cirri at posterior extremities (figure 29, arrows). Pharyngeal fibres about 25 µ m long after silver impregantion (figure 33, arrow).

Remarks: compared with the original description by Foissner et al. (1982), the populations collected from China differ in three ways: a) the undulating membrane appearing as a single (double-rowed) structure (vs. two separated, equally long membranes); b) relatively lower number of fronto-ventral rows (seven to ten vs. ten to 15 (including left and right marginal rows)); and c) number of adoral membranelles (on average 50 or 58 vs. 66).

The structure of the undulating membrane is often difficult to discern in this species due either to the covering of the roof-like structure in the buccal field or to imperfect impregnation. It is thus reasonable to presume that the presence of the two membranes in the original description is either as a result of a form-variation or a misinterpretation.

Morphogenesis during cell division (figures 12–25, 33–48)

Morphogenesis commences with the formation of a long and narrow oral primordium (OP) between the left marginal row and the posterior parts of the frontoventral rows 4 and 5. No parental cirri appear to participate in the formation of the OP (figures 12; 33, arrowhead); meanwhile, the replication bands are recognizable in the macronuclear nodules (figure 12, arrowheads). With the number of basal bodies increasing, the OP is enlarged and stretches to the posterior portion of frontoventral rows 6 and 7 (figures 13; 34,35, arrowhead). The OP continues to grow by the proliferation of basal bodies and differentiates into membranelles at its right anterior end (figure 36, arrowhead); meantime, a streak of loosely arranged basal bodies appears to the right of the OP with its posterior end joining with the OP, this is the undulating membrane anlage (UMA; figures 14, 15, 37, 38, arrowhead). At the same time, some of the cirri in the frontal field dedifferentiate and several streaks of basal bodies develop, forming the cirral anlagen (CA, figures 14; 36, arrows). Later, the CA lengthen; the number of CA and new membranelles increase (figures 15, 37, 38, 43); left marginal row anlage (LMRA) of the proter forms at the anterior end of the old left marginal row (figure 15, arrow), and the old undulating membrane begins to dedifferentiate into the UMA.

Morphogenesis continues with the formation of all cirral anlagen and dorsal kinety anlagen in both proter and opisthe (figures 16, 17, 19); at this stage, the macronuclear nodules begin to fuse (figure 17, arrowheads). In cells with two left marginal rows, each old structure generates one anlage in both proter and opisthe (figures 18, arrowheads; 40, 41, arrows). The new frontal cirri and part of the frontoventral cirri begin to segregate, the leftmost one of which derives from a small anlage separated from the UMA (figures 19, arrowhead; 21, arrows; 39, arrowhead). The macronuclei continue to fuse to a single mass (figures 20; 21, inset; 44, arrowhead).

Unfortunately, the first stage of the development of the dorsal kineties was not observed. However, from our diagrams, we assume that dorsal kineties anlagen are certainly formed within old kineties at two levels, and seem to derive from the separation of a primary primordium originating at the equatorial area (figures 17, 42, arrows; 20).

Figures 22 , 46 show a late division stage with the full number of adoral membranelles. Cytokenesis, division of macronucleus and displacement of the cirri are shown in figures 24, 25, 47, 48. Micronuclei behave like those in other hypotrichs (figures 23, arrows; 24; 45, arrows).

During cell division, no disorganization was observed in the old AZM except for the formation of the UMA in the proter which developed in the same way as in the opisthe; thus, the parental AZM is completely inherited by the proter.

Figures

FIGS. 21–25. Late stages of morphogenesis in Pseudokahliella marina: (21) ventral view, arrows indicating frontal cirrus derived from UMA; inset: fused macronucleus; (22), (23) ventral and dorsal views of the same cell, arrows showing the division of micronuclei; (24), (25) indicating the infraciliature of a late stage. Bars: 50 µm.

FIGS. 37–48. Photomicrographs of middle and late stages of morphogenesis in Pseudokahliella marina: (37), (38) note increase of the number of cirral anlagen and development of oral primordium, arrowhead showing undulating membrane anlage; (39) arrowhead showing the frontal cirrus derived from undulating membrane anlage; (40), (41) infraciliature of anterior and posterior portion of the same cell, arrows showing left marginal row anlagen; (42) arrows indicating dorsal kinety anlagen; (43) infraciliature of ventral side in middle stage; (44) arrowhead showing the fused macronucleus; (45) arrows showing the division of micronuclei; (46)–(48) infraciliature in late stages, arrows showing the division of macronuclei.