Taxonomy of Eudistoma okai (Urochordata: Ascidiacea) Inhabiting the Pacific Coast of Japan, with a Revised Description of Larvae

Abstract

The validity of Eudistoma okai Sanamyan, 2022, proposed as a new replacement name for E. parvum (Oka, 1927), as originally described in the binomen Distoma parva (incorrect original spelling; corrected as D. parvum) and thus a junior primary homonym of D. parvum Sluiter, 1900, is confirmed. The larval morphology (including 3 attachment processes, 4 pairs of lateral ampullae, and a single median ampulla between the ventral-most and middle processes) is revised, based on a re-examination of probable syntypes and other museum specimens of “E. parvum” from Misaki, as well as the examination of new material from the Pacific coast of Japan, and differs from a previous larval description, which lacked the median ampulla. In addition, re-examination of Japanese colonies previously identified as “E. parvum” showed many to have been mis-identified. A morphological comparison of E. okai with seven congeneric Japanese species is included.