Ultrastructure of Helicoprorodon multinucleatum (Ciliophora)

Helicoprorodon multinucleatum has an ultrastructural anatomy like the haptorid ciliates. The somatic monokinetid has two sets of transverse microtubules, an overlapping postciliary microtubular ribbon, and a laterally directed kinetodesmal fiber. Most of the somatic rows of cilia terminate at the anterior end on a peribuccal spiral ridge. Two to three of the somatic kineties continue through the ridge and spiral around the anterior end. Anterior to these spirals are 4-6 concentric spirals or closed rings of single kinetosomes. The kinetosomes in these kineties have the same infraciliary fibers as the somatic kinetosomes and a nematodesma. These kinetosomes are homologous to the oralized somatic kinetosomes found in ciliates in the order Haptorida. Oral dikinetids form a ring surrounding the cytostome. These dikinetids are not the final few kinetosomes of the somatic kineties. The anterior kinetosome of the oral pair is not ciliated and has a transverse microtubular ribbon and a nematodesma. The posterior kinetosome is ciliated and has postciliary microtubules and a ribbon of microtubules that extend into the cytoplasm from the proximal, right side of the kinetosome. The cytostome is closed when the organism is not feeding. Mucocysts and two types of toxicysts are present. The toxicysts are found in the somatic cortex and around the oral region but not within the circle of nematodesmata. There are numerous ovoid macronuclei and micronuclei distributed throughout the cytoplasm. From these results, we may conclude that the genus Helicoprorodon belongs in the order Haptorida.