First record of regular sea urchins Echinothrix calamaris and Astropyga radiata (Echinodermata, Echinoidea, Diadematoida) from shallow-water of Oki Islands, Shimane, Sea of Japan

Abstract

Echinothrix diadema and Astropyga radiata were collected from the Sea of Japan, Oki Islands in Shimane Prefecture, Japan. These two species of Diadematoida are the first records from the Sea of Japan. In this report, the external morphology of both species was described in detail based on the collected specimens. E. diadema and A. radiata are tropical or subtropical species that are distributed in the Indo-West Pacific Ocean and can not invade cold water areas. Therefore, continued research is needed to determine whether the occurrence of these tropical and subtropical animals is due to long-term changes associated with recent increases of seawater temperatures or a temporary effect of warm currents.