Northwestern Pacific ascidians (Tunicata: Ascidiacea). Part 1. Order Aplousobranchia

Abstract

A taxonomy of aplousobranch ascidians from the NW Pacific coasts of Russia, including Bering Sea, Sea of Okhotsk and northern part of the Sea of Japan, is presented. Order Aplousobranchia currently comprises 14 families, 7 of which are repre-sented in the region by at least several species. Sixty-nine species and 19 genera are recognized as valid. Three new genera and four new species are described: Bathyplacentela gen.n., Kussakinia gen.n., Protosynoicum gen.n., Bathyplacentela pedunculata sp.n., Holozoa okhotensis sp.n., H. shimushirensis sp.n., H. urupensis sp.n. A new name Neodiction nom.n. is suggested for Neodictyon Sanamyan, 1998 and Eudistoma okai nom.n. for Eudistoma parvum (Oka, 1927). All known species from this region are included and most of them redescribed based on newly collected specimens and/or on museum material. Many type species are reexamined and illustrated. Identification keys and quality photographic images are provided to simplify a task of species identification for a wide range of biologists. Special attention is paid on nomenclature of discussed families, genera and species, a subject that received little attention from most ascidian experts previously. Several serious long-standing nomenclatural problems were revealed, especially the problems associated with so called “nomina conservanda”, a category uncritically and incorrectly applied to several most widely used generic names in Ascidiacea. Possible solutions of these problems are suggested.