Hemigrapsus Takanoi, New Species, a Sibling Species of the Common Japanese Intertidal Crab H. Penicillatus (Decapoda: Brachyura: Grapsoidea)

The two forms of Hemigrapsus penicillatus (de Haan, 1835), recently distinguished on the basis of electrophoresis and differences in the size of the setal patches on the male chelae, are here recognized as two distinct species. The individuals having smaller setal patches are H. penicillatus, whereas those with larger setal patches are described herein as a new species. Living and fresh material of the two species are also clearly separated by the size and distribution of dark spots on the cephalothorax, abdomen, third maxillipeds, and chelipeds. Morphology of the male first pleopod is different between the two species. Females of the two species are morphologically identical and cannot be easily separated once colour has faded.