Abstract
The intertidal amphipods, which were previously regarded as single species Melita koreana, were studied in the central part of the Inland Sea of Japan. As the result, occurrence of four species (M, koreana, M, rylovae and two unnamed species, sp. I and sp. II) were recognized. M, ryilovae was treated as synonym of U. koreana by Nagata (1965), however, the differences are valid throughout the ontogenetic development, no intermediate form was observed. The four species reported here are distinguishable by morphologyical differences in male gnathopod 1 and female coxal plate 6. The adult body size is also different by species. The amphipods have precopulate habit before mating. Though there was little difference in breeding behavior among the species, no interspecific precopula was observed in cross-breeding experiment. Active selective response of males to females suggested that the males discriminated the conspecific females. These four closely related forms are reproductively isolated each other by ethological mechanism, and should be evaluated as discrete species.
