Cothurnia polydorica sp. nov. (Ciliophora: Peritrichia), a symbiont of shell-boring spionid polychaetes in the Sea of Japan, and a review of ciliates associated with polydorids

Abstract

Small unidentified spionid polychaetes (Polydora sp.) boring in shells of gastropod and bivalve molluscs in the Nakhodka region are hosts of a new species of loricate peritrich named Cothurnia polydorica sp. nov. The large genus Cothurnia can be subdivided into two groups (subgenera or genera) with one or two zooids inside the lorica; C. polydorica is a monozoic (solitary) species; after cell division one of the daughter individuals becomes migratory and swims away. The trophont is not vermiform and thus is not typical of most cothurnids; contraction of fixed specimens is partial, in the adoral half only; the lorica has a second inner layer of material at its base; the stalk is very long as compared with other cothurnids. The migrants adhere to the tips of thick setae of the host but not to its body surface, on which there are scattered small parasitic rhynchodids sucking the host body fluid by short apical tubes. A review of ciliates associated with polydorids is given.