(Sakai, 1974)
The Japanese species of "Pilumnoplax" has long been regarded as conspecific with American Pilumnoplax americana Rathbun, however, when compared with Rathbun's figure of that species, the Japanese species has the carapace depressed and anteriorly more broadened. The front is narrower and produced forwards beyond the level of the orbital region, and its lateral angles separated deeply from the preorbital angle by a deep notch. In American species, no such distinct notch on either side of the frontal margin. The anterior edge of the front is distinctly grooved laterally as in American species.
Antero-lateral borders are apparently shorter than the postero-lateral, arched and posteriorly divergent, and are armed with five acuminate teeth, of which the first or the external orbital tooth is small, the second to fourth are large and the fifth very small.
Chelipeds are robust, markedly unequal; the carpus is armed with two spines at the inner angle; the propodus is inflated, unarmed; both fingers are coloured with deep black, the colour of the immovable finger extends partly onto the under surface of the palm. (Sakai, 1976)
Type locality: Oga Peninsula, Akita Prefecture, Japan.
Range: Japan - Muroto-misaki and Tanabe (Yokoya, 1933), Oga Peninsula, Sagami Bay, Kii Tanabe and Muroto-zaki (Sakai, 1976a), Kyushu-Palau Ridge (Baba, 1986), Wagu (Guinot & Richer de Forges, 1981); Taiwan; 15-700 m.