Zosterodasys

• Somatic cortex. The cell surface is made up of shallow kinetal grooves separated by low cortical ridges. Well-developed alveoli are present beneath the cell surface membrane. Numerous electron-opaque bodies are located in the cortical ridges, inside the kinetal grooves, and are distributed in parallel rows between adjacent kineties. These electron-opaque bodies are approximately 1.0-1.5 um long and 0.50-0.75 um wide. In longitudinal section, they appear ovoid in shape and contain two basic types of material. In some, small, dark rings are evident. In others, there is a concentrated region of electron-opaque material that is usually round in shape. This material is primarily located in the region of the electron-opaque body that is closest to the plasma membrane and it is often surrounded by a less-dense granular material. These electron-opaque bodies apparently form an attachment to the outer alveolar membrane and may extrude their contents outside the cell. No other extrusomes were observed in Z. agamalievi. (ref. ID; 7403)
• Somatic monokinetid. The somatic cilia arise within shallow pits on the cell surface. The kinetosomes of Z. agamalievi do not significantly differ from those of other ciliates except that neither 'A-cartwheel' nor 'B-cartweel' structures are evident in the proximal region of the kinetosome. Instead, the kinetosome appears empty between the terminal plate and base.

• The kinetodesmal fiber originates on triplets five or six of the kinetosome. It extends anteriorly and initially projects toward the cells surface at the sharp angle. It then bends anteriorly and continues for a short distance just below the postciliary microtubules. This fiber terminates before reaching the adjacent kinetosome. The postciliary microtubular ribbon originates from triplet nine and consists of between six and nine microtubules in a row. In transverse sections through the kinetosome, the postciliary microtubules are divergent (<90 degrees to the kinety axis (Williams and Frankel 1973)). Tracts of electron-dense material extend toward the postciliary microtubules from triplets one and six. The postciliary microtubules extend toward the cell surface and curve to continue posteriorly just beneath the alveolar membrane. As they extend toward the cell surface, they bunch up forming a double row and overlap with the postciliaries from adjacent kinetosomes, forming postciliodesmata as they extend posteriorly. The postciliary microtubules extend past approximately five kinetosomes before terminating. The transverse microtubules are the least developed of the infraciliary fibers associated with the somatic monokinetid. Two radially-oriented transverse microtubules are evident. These microtubules are surrounded by electron-dense material in some sections. The transverse microtubules do not overlap with the transverse microtubules of the adjacent kinety. In addition to the three infraciliary fibers described above, a short fibrous root projects anteriorly from the base of the kinetosome into the cell. At least five microtubules extend anteriorly from this rootlet. This rootlet was seen on several kinetosomes but may not be present on all somatic kinetosomes. All three fibers of the infraciliature can be seen in Fig. 15b. Since they originate at slightly differ angles, it is difficult to get all of them in perfect cross-section in the same section. A schematic diagram of the somatic monokinetid shows the orientation of the postciliary microtubules, kinetodesmal fiber, and transverse microtubules relative to each other and to the basal body. (ref. ID; 7403)
• Synhymenium. The synhymenium consists of a row of dikinetids that extends obliquely along the ventral surface of Z. agamalievi. The cell membrane of the cilia of the synhymenium is modified with two folds that resemble projections in cross-section. The function of these modification is not known but may coordinate ciliary beat in the synhymenium or indicate these are sensory cilia. A electorn-dense material connects the two kinetosomes of the dikinetid. It extends from triplets eight and nine of the anterior kinetosome to triplets four and five of the posterior kinetosome. The anterior kinetosome has a postciliary microtubular ribbon of two microtubules that originates from triplet nine. There is no evidence of a kinetodesmal a fiber or transverse microtubules associated with the anterior kinetosome.
• The posterior kinetosome has a ribbon of eight to nine postciliary microtubules. In transverse sections through the kinetosome, the postciliary ribbon is divergent (<90 degrees to the kinety axis (Williams and Frankel 1973)). Tracts of electorn-dense material extend from triplet seven or eight and one toward the postciliary microtubules. Outside the electron-dense material extending from triplet one is another tract of electron-dense material that resembles a comb, with the teeth of the comb extending toward the fiber of electron-dense material located adjacent to the postciliary microtubular ribbon.
• The posterior kinetosome also has a kinetodesmal fiber. The kinetodesmal fiber extends a short distance and terminates to the right of the anterior kinetosome of the posterior dikinetid. There is no evidence of a transverse microtubular ribbon associated with the posterior kinetosome. (ref. ID; 7403)
• Organization of the oral area. The cytostome-cytopharyngeal complex is a prominent feature that is located in the anterior region of the cell, on the mid-ventral surface. The opening to the cytostome-cytopharyngeal complex lies at the base of a shallow atrium. No cilia are associated with any part of the oral apparatus in the feeding stage of the life cycle examined in this study. Electron-opaque bodies, similar to these observed in the somatic cortex, are also found around the mouth region.
• The cytopharynx is lined by two sets of microtubules. The first set of microtubules are found in bundles as nematodesmata; approximately 15 nematodesmata support the cytopharynx. In cross-section, the nematodesmata appear as round rods of hexagonally packed microtubules. At their distal ends, the nematodesmata are capped with a striated, electron-dense capitulum. A capitulum covers the distal-most part of each nematodesmata, and initially extends toward the surface of the cell. It then turns in sharply toward the interior of the cytopharynx giving the whole structure (nematodesmata and capitulum) the appearance of a sock when viewed from the side. The second set of microtubules are arranged as rows (lamellae) which originate at the lip of the atrium, curve over the lip of the atrium, and then descend down into the cytoplasm, forming the inner lining of the cytopharynx. In cross-section, the microtubules appear to curve as they extend into the cell, terminating at the base of the nematodesmata where they contact and partially wrap around the nematodesmata in groups of four to seven. Between the ring of nematodesmata and the microtubules lining the cytopharyngeal tube, an electron-dense fibrous sheath surrounds the cytopharynx. Distally, the sheath extend up to the surface of the cell and terminate before reaching the plasma membrane. Proximally, it extends approximately half-way to the proximal-most part of the cytostome-cytopharyngeal complex. The cytoplasm between the nematodesmata and the fibrous sheath is dominated by intrapharyngeal phagoplasm near the surface of the cell but toward the base of the cytopharynx, the fibrous sheath and nematodesmata become situated more closely together so that no cytoplasm is evident between them. (ref. ID; 7403)
• The endoplasm. The ectoplasm of Z. agamalievi is separated from the endoplasm by a thin tela corticalis. The tela corticalis is a distinct fibrillar layer that forms a continuous network around the cell surface just proximal to the basal bodies of the cilia. Beneath the tela corticalis are numerous mitochondria with tubular cristae. Mitochondria are also distributed throughout the endoplasm and are present in particular abundance near the synhymenium. The single macronucleus is of the homomerous type. It is generally ovoid and may become curved into the shape of a crescent. Several nucleoli are evident within the nucleoplasm of the macronucleus and the heterochromatin is globular and evenly distributed. Nuclear pores are evident in the envelope of the macronucleus. An ovoid-shaped micronucleus is located adjacent to the macronucleus. The contractile vacuole system lies within the endplasm, just below the tela corticalis. In Z. agamalivei, the contractile vacuole system is comprised of a pore that opens to the exterior, a main contractile vacuole, and a system of collecting tubules. There appear to be two main systems of tubules, one on each side of the contractile vacuole. These tubules connect to and presumably release their contents into the contractile vacuole. The main vacuole is connected to the surface by a single pore which is formed by an indentation of the plasm membrane. The contractile vacuole system is supported by two sets of microtubules. One set, the helical pore microtubules (Patterson 1980), surround and support the pore. The other set, the radial pore microtubules (Patterson 1980), extend from these and run along the collecting canals. Mitochondria are close to the surface of both the contractile vacuole and collecting tubules. (ref. ID; 7403)

Examined material