Rehabilitation of two deep-sea holothurian species in genus Pannychia from the northwest Pacific Ocean

Abstract

Genus Pannychia Théel, 1882 is one of the dominant sea cucumber genus in the bathyal zone of the North Pacific Ocean. Previously seven species/subspecies were described in Pannychia and another closest genus Laetmophasma Ludwig, 1894 from all over the Pacific Ocean, but all of them were synonymized into Pannychia moseleyi Théel, 1882, which is currently single valid species in the Pacific Ocean. In this study, we rehabilitate Pannychia henrici Ludwig, 1894 and Pannychia virgulifera Ohshima, 1915 as separate species from the northwest Pacific Ocean, which were originally established as geographical variation/subspecies of P. moseleyi. This study includes molecular phylogenetic analysis based on specimens collected from broad part of the northwest Pacific Ocean, and morphological comparison including re-examination of both subspecies type specimens. Genetically these two northwest Pacific taxa and P. moseleyi are clearly distinguished from each other, which corresponded to different characteristics of dorsal papillae arrangement, the body coloration, and the ossicle density in dorsal body wall. As a result of rehabilitation of P. henrici and P. virgulifera, the genus Pannychia was reorganized to 4 valid species, but P. moseleyi still include large morphological variations, and it is necessary to a further taxonomic revision. Additionally, P. henrici and P. virgulifera particularly represent an example of importance of body coloration in taxonomy of the deep-sea Holothuroidea.