de Haan, 1833
The original description of this species given by de Haan is too brief and the figure is also by no means a good representation, however, after a careful examination of a large series of specimens of Pilumnus obtained from various localities in Japan, I came to the conclusion that the early-known Pilumnus hirsutus Stimpson and Pilumnus habererimus Doflein are only synonymous with this species. The main characters of this species are as follows:
The carapace transversely oval, the dorsal surface strongly convex from before backward but slightly so from side to side; it is covered with short fur but in some specimens there are some additional long and feathered hairs, which are disposed in tufts. The front is bilobate, the lobules being convex and finely denticulated and externally divide from the orbital border by a shallow notch. The antero-lateral borders are very slightly shorter than the postero-lateral, the former with three spines which are longer and sharper in relatively larger specimens, but in some specimens, they have accessory spinules; the postero-lateral borders are less concave. The external angle of the orbit is also developed into a spine, but it is smaller than those on the antero-lateral border. The infraorbital border is finely denticulated.
The chelipeds of this species are extremely unequal, the palm of the larger cheliped dorsally granulated, its external surface is only granular near the upper border and the proximal end, the remainder of the surface is glabrous; between these granules are disposed long hairs, but in full-grown male specimen the hairs are very often worn out. The smaller cheliped has the wrist and palm armed with numerous sharp spinules, interspersed with long setae. The ambulatory legs are thin and slender, merus unarmed, while the carpus has a sharp spinule at the distal end of the anterior border.
With regard to synonymy, Pilumnus hirsutus Stimpson was united with the present species by Parisi (1916), but afterwards again separated by Balss (1922, 1933). According to Stimpson, P. minutus differs from hirsutus mainly on account of the convex postero-lateral borders, the smooth carapace, and slender and little hairy ambulatory legs. In Stimpson's figure, the small cheliped has the wrist and palm markedly spinulated on denudation, but this is probably only due to the schematic representation of the character. In the photograph of P. hirsutus, given by Rathbun (1923) and also that of Pilumnus habererimus Doflein (which is, according to Balss, synonymous with Pilumnus hirsutus) the spinules of the small cheliped occur as thickly as in P. minutus before me. The spinule at the distal end of the carpus of the ambulatory legs, which was not figured by Stimpson, has been mentioned by Balss (1933). (T. Sakai, 1939: 535)
Type locality: Japan.
Range: Red Sea (Nobili, 1906); South Africa - False Bay, Algoa Bay, off East London and off Port Shepstone (Barnard, 1950); Persian Gulf - off Bahrain (Stephensen, 1945); Amirante Islands (Rathbun, 1911), Providence Islands (Rathbun, 1911); Maldives - Male Lagoon (Rathbun, 1902b); Sri Lanka - Trincomalee (Balss, 1933b); Andaman Islands (Alcock, 1898, Sankarankutty, 1962); Mergui Archipelago (Alcock, 1898, Chopra & Das, 1937); Strait of Malacca (Alcock, 1898); Japan - Kobe (Miers, 1886), Kagoshima (Ortmann, 1893), Sagami Bay (Doflein, 1902, Sakai, 1965b), Amami-Oshima and Ogasawara-shoto (Stimpson, 1907), Tokyo Bay and Sagami Bay (Parisi, 1916), Mutsu Bay (Yokoya, 1928), Hakodate and Tsugaru Strait (Balss, 1933b), Inubo-zaki, near Tanabe, Ashizuri-misaki, Bungo Strait, Tanegashima, and Goto-retto (Yokoya, 1933), Nagasaki (Sakai, 1934a), Shimoda (Sakai, 1935), Iwate Prefecture, Tateyama Bay, Shimoda, Ise Bay, Nanki Shirahama and Nagasaki (Sakai, 1939), Iyo Strait, Tottori Prefecture, Fukuoka Prefecture, Amakusa and Nagasaki (Takeda & Miyake, 1968a), Tsushima Strait and Genkai-nada (Takeda, 1973), Amakusa (Yamaguchi et al., 1976), Mage-jima, Kagoshima Pref., (Takeda, 1977b), from Aomori Bay to Kyushu and Amami-shoto (Sakai, 1976a), Shiono-misaki (Takeda, 1979a), Oshima Passage, Amami-Oshima (Takeda, 1989), Oshoro and Hakodate Bay, Hokkaido (Komai et al., 1992), Suruga Bay (Takeda, 1997), off Matsuyama and off Takehara, Seto Inland Sea (Takeda et al., 2000); Korea - Korean Strait (Miers, 1879b), Ullung do, Kanzan-to and Cheju-do (Kamita, 1941), Cheonbu, Eocheong Iland, Jang-gun Island, Bangjugpo, Mijo Ri, and Hoeng-gan Island (Kim, 1973), Cheju-do (Kim & Chang, 1985); Northern China Sea (Stimpson, 1907); China - Guangdong and Shandong Peninsula (Dai & Yang, 1991); Taiwan Strait (Balss, 1933b); Macclesfield Bank (Balss, 1933b); Gulf of Thailand (Rathbun, 1910a, Balss, 1933b); Singapore (Balss, 1933b, Lanchester, 1900); Philippines - (Balss, 1933b), Romblon, Taratara Id., Nagubat Id., Gulf of Davao, Manila Bay, Tanguingui Id., Bataan Island, between Samar and Leyte (Garth & Kim, 1983); Sulu Archipelago - Balukbaluk Island, Jolo, Sulade Island, Tinakta Island, and Observation Island (Garth & Kim, 1983); Indonesia - Ambon and Kepulauan Kai (Balss, 1933b), Buton Strait (Garth & Kim, 1983); Australia - off Holbourne Island (Haswell, 1882c), off Bowen and off Double Island Point (Rathbun, 1923a), Moreton Bay (Campbell & Stephenson, 1970); New Caledonia (A. Milne Edwards, 1873); littoral to 276 m.