Mothocya kaorui n. sp. (Crustacea: Isopoda: Cymothoidae), a fish-parasitic isopod with unique antennules from the Izu Islands, Japan.

A new species of fish-parasitic isopod in the family Cymothoidae is described from the Izu Islands, Japan. Mothocya kaorui n. sp. is reported from the gill cavities of the keeled needlefish, Platybelone argalus platyura (Bennett). Despite its unique morphological characters, such as completely article-fused antennules, mitochondrial DNA analysis indicated that it belongs to Mothocya Costa. The new species is clearly distinguished from all other species of Mothocya by having completely fused, stout antennules and partially fused, slender antennae; maxilla mesial lobe with 3 or 4 recurved robust setae, lateral lobe with 4-6 recurved robust setae; maxilliped with 5-8 robust setae on article 3; coxae 2 and 3 wide; black subtriangular pleotelson; and black uropods.
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