A new species of the genus Arhynchite (Annelida, Echiura) from sandy flats of Japan, previously referred to as Thalassema owstoni Ikeda, 1904

Masaatsu Tanaka,Teruaki Nishikawa

doi:10.3897/zookeys.312.5456

Abstract

A new echiuran, Arhynchite hayaoi sp. n., is described from newly collected specimens from sandy flats of the Seto Inland Sea, Japan, together with many museum specimens, including those once identified as Thalassema owstoni Ikeda, 1904 or Arhynchite arhynchite (Ikeda, 1924). The new species is clearly distinguishable from its congeners by the smooth margin of gonostomal lips and lack of rectal caecum. Brief references are also made to the morphological distinction between the new species and Thalassema owstoni, originally described from the deep bottom on the Japanese Pacific coast.

Highlights

Echiurans are a small group of marine coelomates, previously classified as a distinct phylum, but often included in the Phylum Annelida on the basis of recent molecular phylogenetic analyses (McHugh 1997, Bleidorn et al 2003, Struck et al 2007, 2011).Copyright MasaatsuTanaka,Teruaki Nishikawa
Further materials have been retained at our Laboratory of Taxonomy, Toho University (LTTU), the Department of Zoology, University Museum, University of Tokyo (UMUTZ), or Tohoku University Museum (TUM)
It is possible that A. hayaoi is widely distributed in the Seto Inland Sea and the Pacific coasts of Middle Japan, whereas A. arhynchite, with its type locality probably originating near Hokkaido (Ikeda 1924, Satô 1937), is restricted to cold northern waters

Summary

Introduction

Echiurans are a small group of marine coelomates, previously classified as a distinct phylum, but often included in the Phylum Annelida on the basis of recent molecular phylogenetic analyses (McHugh 1997, Bleidorn et al 2003, Struck et al 2007, 2011). Many taxonomic problems remain unsolved, one of which concerns an echiuran called “kouju” in Japanese (probably meaning “good bait”). This echiuran was once abundant and collected in great numbers from intertidal or subtidal sandy bottoms for fish bait in the Seto Inland Sea, Japan (Mori et al 1932, Ishikawa 1938); its density has lately declined too greatly for such use (Nishikawa 2007, 2012, Saito et al 2011). We describe “kouju” as a new species of the genus Arhynchite Satô, 1937

Materials and methods

Discussion