CONTRIBUTION TO THE STUDY OF THE HYSTEROC INETID CILIATES - THE GENUSPREPTYCHOSTOMUM DE PUYTORAC, 1968

Three species of the genus Preptychostomum, found in the digestive tra ct of oligochaetes (g. Alma) were described from silver stained prepar ations. The two new species, P. microstomum and P. magnum differ from P. katashimae by their shape and oral apparatus extent ; however, all of them have a similar buccal organization. Ultrastructural observatio ns on P. microstomum reveal some characteristics of the somatic cortex (flattened alveoli, a thin epiplasmic layer, a granular ectoplasm, a thick ecto-endoplasmic boundary) and of the somatic kinetid (monokinet id with hyperdivergent postciliary ribbon) that are common for all the hysterocinetids. The oral infraciliature consists of a long paroral o rganelle (stichodyad) and 3 adoral organelles (AD1 and AD2 with two ro ws of kinetosomes, AD3 with one row). This study confirms the,unity of the plan of organization of the hysterocinetids.