de Haan, 1841
The carapace is circular and globular, very slightly longer than broad; its upper surface is covered with granular patches mainly on the branchial regions and also along the median line, which is usually marked by a longitudinal row of larger granules. The branchio-cardiac grooves are almost rudimentary, they are only marked by depressed smooth surfaces, which have sometimes a few granules and small pits.
The front is narrow and medially depressed and grooved, so that it appears distinctly bidentate when the animal is observed obliquely from backward or forward. The epistome is markedly projecting beyond the edge of the front; anterior boundaries of the pterygostomial regions are also visible from above, and are cleft near the outer angle. The antero-lateral and postero-lateral borders are marked by a rim of granules, some of which at regular intervals are distinct. The posterior border is subtruncate in the male but almost rounded in the female.
The exopodite of the external maxillipeds are broad and foliaceous; merus and ischium are smooth to the naked eye; in the case of the female, these segments have a row of hairs along their inner borders.
The chelipeds are very stout; the arm is somewhat depressed and granulated on the upper proximal surface and also along the anterior and posterior borders. The palm is longitudinally ridged in the median line, which is granulated as well as the inner and outer edges; between the median and the inner edges, there is also a line of minute granules. The fingers are compressed, their cutting edges are finely and regularly denticulated in their whole extent. The ambulatory legs are smooth and gradually decrease in length from first to last; the merus and carpus are subcylindrical, but the propodus and dactylus are depressed, the latter is lanceolate in shape. The abdomen of male consists of three pieces as usual, the second tergum being completely fused with the third tergum in its middle. Female abdomen is very smooth and glabrous except the first three terga and the distal surface of the penultimate tergum. (Sakai, 1937)
Type locality: Japan.
Range: Japan - (de Haan, 1841), Tokyo Bay (Ortmann, 1892), Shimoda (Sakai, 1935), Iwate Prefecture, Tateyama Bay, Inage, Misaki, Shimoda, Ise Bay, Nanki Shirahama, Onomichi, and Nagasaki (Sakai, 1937a), Amakusa, Sea of Ariake and Tsuyazaki (Miyake et al., 1962), Sagami Bay (Sakai, 1965b), Tokyo Bay, Sagami Bay, Shimoda, Kii Nagashima, Kii Minabe, and Shimabara Peninsula (Sakai, 1976a), Amakusa (Yamaguchi et al., 1976), Fukuoka (Miyake, 1983), Tokyo Bay, Kii Minabe, Nanki Shirahama, Tosashimizu, Shimabara, and Ariake Sea (Muraoka, 1998), Amami-shoto; Korea - Keisho-nando, Zenra-nando, Zenra-hokudo, Keiki-do, Kokai-do, Heian-nando, and Heian-hokudo (Kamita, 1941), Daecheon, Daeyeonpyeong Island, Yeong-jong Island, Jag-yag Island, Deogjeog Island, Bi-geum Island, Gyeogpo Ri, Yeosu, and Mogpo (Kim, 1973); China - Liaodong Peninsula, Liaodong Bay, Bo Hai Gulf, and Shandong Peninsula (Shen, 1932), Shanghai, Ningbo, Chuanshih, Santuao, Fuzhou, Tsimei, and Xiamen (Shen, 1940b), along the shore from Guangdong to Liaodong Peninsula (Dai & Yang, 1991); Taiwan - Wuch'i, Yensuikang, and Chiukang (Lin, 1949); Singapore; Philippines; west America - Puget Sound; sandy or muddy flats, between high and low tidal marks.