A New Species of Massinium (Echinodermata: Holothuroidea: Dendrochirotida: Phyllophoridae: Semperiellinae) from Western Japan

A new dendrochirotid sea cucumber, Massinium japonicum sp. nov., is described from areas in western Japan, including the middle of the Seto Inland Sea, west of the Sea of Japan, the shore of the Amakusa Peninsula, and the shore of the Kii Peninsula. The ossicle assemblage of the new species (M. japonicum) is similar to that of M. maculosum Samyn and Thandar, 2003, the type species of Massinium Samyn and Thandar, 2003. However, the new species is readily distinguishable from M. maculosum and its congeners by the absence of rod/elongated rosette ossicles in the tentacles. The tentacle ossicles of the new species comprise only oval, simple, open rosettes, 20–40 µm in length, while the other congeners possess rods/elongated rosette-shaped ossicles in the tentacles (very rarely also table ossicles). This new species has been collected from the shallow waters of western Japan living amongst boulder area in the intertidal-subtidal zone, at a depth of approximately 0–20 m.