Actumnus ngankeeae sp. nov. and Pilumnus swajayai Ng & Rahayu, 2021, pilumnid crabs from Japan (Crustacea: Decapoda: Brachyura)

Abstract

New and rare crab species of the family Pilumnidae, Actumnus ngankeeae sp. nov. and Pilumnus swajayai Ng & Rahayu, 2021, are reported from Japan. Actumnus ngankeeae from the Ogasawara (Bonin) Islands is characterized by the following features: the carapace is transversely ovate and strongly convex longitudinally and transversely; the dorsal surface is uniformly covered with small granules and sparse short setae, with the regions defined by narrow furrows; the anterolateral margin is narrowly crested along its whole length and separated into four convex lobes by three V-shaped notches. Both chelipeds are stout, with short, strongly curved fingers. Its specific affinity to A. obesus Dana, 1852, is briefly discussed. Pilumnus swajayai from the Ryukyu Islands is wholly covered with tomentum; the carapace anterolateral margin is armed with three sharp teeth directed obliquely forwards, the second of which is the largest; the subhepatic tooth is distinct, but smaller than the carapace anterolateral teeth; the hepatic region is armed with a dentiform lobe; both chelipeds are armed with scattered conical granules on the carpi and palms; and the ambulatory legs are armed with some spinules on the dorsal margins of the carpi and propodi. The generic affiliation to Pilumnus is acceded to the original description after discussion on the related genera. The present record of P. swajayai from the Ryukyu Islands is the second since the original description from Indonesian waters.