(Sakai, 1938)
The carapace elongate pyriform; the gastric region extremely convex, especially in full-grown specimens. The pseudorostral spines are well divergent and strongly deflexed so as to be continuous with the anterior declivity of the gastric region; they are basally broadened and have an indistinct lobular angle near the middle of the inner border.
There are five tubercles (at least they are constant in number in our specimens but in Balss' specimen they are decribed as four), which are arranged in the median line of the gastric region and two flat ones on either side of this row; the cardiac region is mounted with four small tubercles forming a quadrangle. The intestinal region has a large tubercle in the middle and two side by side in front and in rear of it. There is a large low tubercle on each supraocular eave, which is covered with curled hairs. The hepatic regions are mounted with about ten tubercles, of which two at outer angle and another two below these are larger; the branchial regions have sixteen to eighteen tubercles, of which several marginal ones are larger and erect. These tubercles are invariably furnished with curled hairs, which help the animal to attach numerous sea weeds or hydroids, with which the animal is protected from attack.
The supraocular eaves are somewhat ventrally hollowed and their posterior angle produced into an acuminate tooth but with no preocular spine at all. No intercalated spine but the postocular spine is broad and acuminate at tip. The sternum of the male is broadly canaliculated on either side at the base of the chelipeds, the inner ridge of each canaliculation being furnished with hairs.
The eyestalks are very slender and thin, cornea oblique and scarcely swollen. The basal segment of antenna has a prominent tooth at the antero-external angle, which projects obliquely forwards. Chelipeds are not very stout, arm has usually three tubercles on the upper border, wrist has an indistinct carina on the outer border and its inner border is fringed with long setae; palm is distally narrowed, fingers do not much gape, the cutting edges being uniformly denticulated.
Ambulatory legs are rather stout and thickly covered with long setae, interspersed with curled hairs especially along the anterior borders. The dactylus is strongly hooked at tip. (Sakai, 1938)
Type locality: Shimoda, Japan.
Range: Japan - Shimoda (Sakai, 1935), Shimoda, Tateyama Bay, Gobo and Nagasaki (Sakai, 1938a), Hachijo-jima (Sakai, 1954), Sagami Bay (Sakai, 1965b), Tokyo Bay, Sagami Bay, Shimoda, Kii Nagashima, Kushimoto, Shiono-misaki, Kii Minabe, and Nagasaki (Sakai, 1976a), Tobishima, Yamagata Prefecture (Suzuki S., 1979), Kachiyama, Uraga Canals (Griffin & Tranter, 1986a), Manazuru, Shimoda, Kii Nagashima, Gobo, Kii Minabe and Tosa Bay (Muraoka, 1998).