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.
