Descriptions and ecological notes of free-swimming forms of cymothoid isopods (Crustacea: Peracarida) collected in two coastal waters of Japan

Abstract

Abstract.— The objective of the study is to clarify the knowledge of free–swimming forms of cymothoid isopods, ectoparasites of fishes, collected in two coastal waters of Japan. The sampling was carried out in two ways, light–trap samplings at night in Osaka Bay, Pacific coast of central Honshu and direct observations and collections in the daytime in the coastal water of Izu–Ohshima Island, Sagami Sea. A total of 326 cymothoids was collected from both localities and they were identified as three morphotypes of mancae, unidentified early juvenile, and juveniles of three genera: Nerocila Leach, 1818, Anilocra Leach, 1818 and Mothocya Hope, 1851. Morphological characters of them were described in detail, and problems in the identification were discussed. The body shapes and the serrations on inner margins of the dactyli of pereopods are the most important characters to divide mancae. In addition, the seasonal occurrence and the swimming behavior of them are also reported. IntroductionCymothoid isopods (Crustacea: Peracarida) are ectoparasites of marine, brackish and freshwater fishes (Brusca, 1981). Mature females and males infect in the buccal, branchial or abdominal cavity or attach on the body surface of the hosts; on the other hand, mancae, the spawned stage in the brood pouch of adult females, have been spending a planktonic period after released from the adult female to continue for early juvenile, then, late juveniles infect host fishes (e.g. Brusca, 1978). Currently, over 360 species in 43 genera of the family Cymothoidae have been recorded in the world (Bruce & Schotte, 2013), and about 50 species are known from Japan and its adjacent waters (Saito