SELENIDIUM-PENNATUM SP-N - A NEW SPECIES OF ARCHIGREGARINES FROM FLABELLIGERA-AFFINIS (POLYCHAETA, FLABELLIGERIDAE)

A new species of Archigregarinida, Selenidium pennatum sp. n., from one of the White Sea polychaetes is described. S. pennatum inhabits the stomach of the sublittoral worm Flabelligera affinis. Mature trophozoites elongated and flattened on each side, up to 160 X 36-mu-m, with the pointed anterior and rounded posterior end. The nucleus at about the middle of the body, spherical, 14-26-mu-m in diameter, with a spherical nucleolus. Mature trophozoites immovable, young ones bend very seldom. Syzygy caudal, 208-230X29-33-mu-m, immovable, nuclei are not visible. In contrast to the other species of this genus Selenidium pennatum has no longitudinal pellicular striations. The ultra-structural data permit to attribute the new species to the order Archigregarinida.