A new genus and new species of endoparasite (Isopoda, Entoniscidae, Diogenioninae) from the hermit crab Diogenes izanamiae in southwestern Japan.

Abstract

Species of Entoniscidae are endoparasitic isopods that parasitize a variety of decapod crustaceans. Entoniscid parasites of the subfamily Diogenioninae, which was represented by a monotypic genus, are a small group of endoparasites of hermit crabs and have previously been reported only from the Red Sea and the Philippines. During a survey of the subtidal zone at Usa, Kochi, southwestern Japan, an undescribed species of the subfamily was discovered inhabiting the visceral cavity of the hermit crab Diogenes izanamiae Asakura, 2006. Detailed morphological examination revealed that this species differs from the sole species in the only previously known genus of the subfamily, Diogenion, in having a brood pouch formed by overlapping oostegites 1-7 and in possessing uniramous pleopods on pleomeres 1-4 in females. On the basis of these diagnostic characters, a new genus and species, Paradiogenion japonica n. gen., n. sp., are established and described herein, based on adult females, males, and epicaridium larvae. The new genus exhibits several primitive morphological characters and is considered the ancestral taxon within Entoniscidae. This study represents the first record of Diogenioninae, as well as of entoniscid isopods parasitizing hermit crabs, from Japan and provides a key to understanding the parasitic adaptations of the family Entoniscidae.