New species of Ilyograpsus from the Ryukyu Islands, Japan, with notes on I. nodulosus Sakai, 1983

A new species of the genus Ilyograpsus is described from the Ryukyu Islands. Ilyograpsus paantu, new species, can be easily distinguished from all congeners by its longitudinal postfrontal cristae and relatively longer carapace. Ilyograpsus nodulosus was originally described from damaged juveniles, there had been no information on adult males. Present study provides diagnosis of the species based on topotypic specimens, including adult males, and compares the species with all congeners.