A new peltogastrid rhizocephalan parasitising a hermit crab from the Japanese coast: a second species of Dipterosaccus Van Kampen & Boschma, 1925 (Crustacea: Cirripedia).

A new rhizocephalan species of the genus Dipterosaccus Van Kampen & Boschma, 1925, is described from the host hermit crab Calcinus vachoni Forest on the coasts of mainland Japan and the Ryukyu Archipelago. Dipterosaccus shiinoi n. sp. differs from the previously described species, D. indicus Van Kampen & Boschma, 1925, which is redescribed, principally in the morphology of the mantle aperture and the disposition of the receptacle ducts. The distribution ranges of the two species partly overlap and they are sympatric at the same reef site near Okinawa Island. Their differentiation as two distinct species was confirmed by partial sequences of the COI gene. The monophyly of Dipterosaccus is supported by high Bayes posterior possibility and bootstrap values.