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

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 congeners, 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 Herouard, 1889, and T. venusta Selenka, 1867, species for which detailed description of ossicles are lacking.