This is a very small species, of which, however, a sufficient number of examples were taken to illustrate it fully. The carapace is very broad, with a hard, smooth, ivory-like surface. Proportion of length to breadth, 1: 1.75. Sides evenly rounded, tumid, with a slightly raised horizontal marginal line or crest, the antero-lateral portion of which is armed with two or three very minute, inconspicuous teeth. Front broad, straight, slightly pointed at the middle. Orbits small, rounded, margins entire. Subhepatic regions swollen. Endostome divided by a ridge on either side. Buccal area short, very broad in front and narrowed behind. External maxillipeds nearly as in Carcinoplax longimana, except that the exognath is broader, with a spiniform tooth, and the outer margin of the endognath is deeply concave; the meros is much broader than the ischium and much produced at its external apex or auricle; finally the palpus is rather endarthroid than goniarthroid. Chelipeds long and slender, with glossy surface; meros slightly hairy on the edges; carpus small; hand elongated with a smoothly-rounded and somewhat swollen palm; fingers slender, as long as the palm, sharply dentated within, teeth small, tips hooked, crossing each other. Ambulatory legs slender, with hairy edges. Abdomen of the male triangular, median segments soldered, margin toothed at base. Abdomen of the female triangular.
The colour in life is pale frownish or yellowish; three diverging white streaks on the posterior part of the carapace; chelipeds darker; beneath white. Dimension of the carapace in male: Length, 0.16, breadth, 0.28 inch. (Stimpson, 1907)
Type locality: Ogasawara-shoto.
Range: Japan - Ogasawara-shoto (Stimpson, 1858b, 1907).