ON PARAPTYCHOSTOMUM-ALMAE N-G, N-SP, A COMMENSAL CILIATE FROM THE DIGESTIVE-TRACT OF OLIGOCHAETES OF THE CAMEROONS, IN A NEW SUBCLASS HYSTEROCINETIA

Morphological and ultrastructural studies on a new ciliate, Paraptycho stomum almae, from the digestive tract of an oligochaete (Alma emini) from the Cameroons are carried out. The flattened cell has a large siz e; its left lateral face bears an anterior thigmotactic zone that incl udes seven-nine short kinetal segments. The somatic cortex is composed of flattened alveoli, a thin epiplasm and a microfibrillar ecto-endop lasmic boundary. Kineties are made of monokinetids, each particularly characterized by a long anteriorly directed kinetodesmal fiber, and a hyperdivergent postciliary ribbon. The postero-ventral buccal apparatu s consists of a short peristome and a deep longitudinal infundibulum. The paroral organelle is a long stichodyad. The three adoral organelle s are of different types: AD1 and AD3 are of the membranoid type, resp ectively with two and one rows of ciliated kinetosomes; AD2 is of the peniculus type with six-seven rows of ciliated kinetosomes. A microfib rillar network with nodes arises from all the buccal kinetosomes and e xtends under the naked wall. Mitochondria are small and numerous and d ispersed throughout the whole cell. The existence of an AD2 with more than two rows of kinetosomes warrants the creation of the new genus Pa raptychostomum and a new family, Ptychostomatidae. The presence of a d istinct ecto-endoplasmic boundary and of somatic kinetids exclusive wi thout transversal dense tractus, hyperdivergent postciliary ribbons, a nd dispersed numerous mitochondria, added to particularities of the st omatogenesis, allow us to clearly separate hysterocinetians from the s cuticociliates and to set up for them the new subclass Hysterocinetia, within the class Oligohymenophorea, with a single new order Hysteroci netida.