A New Species of Thyone (Echinodermata: Holothuroidea: Dendrochirotida: Phyllophoridae) from Wakayama, Japan

Abstract

A new phyllophorid sea cucumber, Thyone susamiensis sp. nov., is described from the intertidal zone of the south coast of Wakayama Prefecture, western Japan. It is distinguished from the most of its congeners by the absence of ossicles in the body wall. Thyone susamiensis has only rosette-like ossicles in the introvert, where table-like ossicles are usually observed in other Thyone species. The usual table-like ossicles were observed only in the peri-oral skin in T. susamiensis. Among conge- ners, this condition has been reported only in Thyone flindersi O’Loughlin, Barmos, and VandenSpiegel, 2012. However, T. flindersi occasionally has table-like ossicles in the anal appendages, where T. susamiensis usually only has rod-like ossicles. The general body colouration and the shape of the calcareous ring are also distinctive, separating species T. susamiensis from T. discolor Sluiter, 1901, T. roscovita Hérouard, 1889, and T. venusta Selenka, 1867, species for which detailed descrip- tion of ossicles are lacking.