Revision of the Turbellarian Genus Ectocotyla (Seriata, Monocelididae) Associated with the Crabs Chionoecetes opilio and Hyas araneus

Abstract

Ectocotyla hirudo (Levinsen, 1879) is redescribed and recorded for the first time from the gills and branchial chambers of Chionoecetes opilio and Hyas araneus. Problems arising from previous descriptions are resolved through comparison of freshly collected material, at different times of the year, with type material of Coleophora sp. and the type material of E. paguri Hyman, 1944, both of which are shown to be identical to the present material. Accordingly, E. paguri Hyman, 1944 is regarded as a junior synonym of E. hirudo (Levinsen, 1879). A new species, E. multitesticulata, is described and recorded also from C. opilio and H. araneus. Ectocotyla multitesticulata differs from E. hirudo primarily in the larger size of the worm, the greater number and size of the testes, the size of the egg capsule, and in the differences of the karyotype. The genus Ectocotyla is discussed in relation to closely related genera (Peraclistus, Minona, and Preminona) in the family Monocelididae. Key words: turbellarian systematics, Proseriata, Monocelididae, Ectocotyla, crab commensal