[Morphology and biology of cystophorous cercariae from the Bering sea].

Three new species of cystophorous cercariae, Cercaria appendiculata Pelseneer, 1906, C. octocauda Tschubrik, 1952 and C. saccocaudata Tschubrik, 1966, are described from the gastropod Tectonatica clausa (Broderip et Sowerby). C. saccocaudata is a larva of trematodes of the genus Lecithaster. The development of parthenites of this species carries out within one summer season. Parthenites of C. appendiculata and C. octocauda are capable to survive unfavourable winter conditions and produce cercariae in the next summer. The above three species were found to eject cercariae through the ejaculatory tube which is an important adaptation of chemiurids to the infection of the second intermediate hosts.