Percnon planissimum

(Herbst, 1804)

Carapace thin, slightly longer than broad, covered with short bristles, some symmetrical raised patches naked. Front narrow, 4-toothed, the median pair deflected. Innerorbital angle with 3 teeth. Dorsal orbital border finely denticulated. Ventral orbital border finely serrated. Ventral innerorbital angle blunt, tooth-like. Epistome with 3 spines; the median one large, each lateral one small, about half the length of the middle tooth. Antero-lateral margin with 4 teeth including the outerorbital angle, regularly decreasing in size.
Chelipeds are of various types, depending on individuals and sexes. Merus slender, with a row of short spines, the ventral inner border with 2 subdistal sharp spines and a distal obtuse spine, the ventral outer border with 3 distal spines. Carpus small, with 2 rows of short spines. Palm high and compressed, about as long as broad, its surface smooth. Fingers shorter than palm, spoon-shaped at the tip. Ambulatory legs slender. Coxa of the last legs without spines. Merus of the first legs narrower, the remaining meri broader. All meri with a row of short teeth on their anterior border, the posterior border with a distal sharp tooth. Merus of the first 3 ambulatory legs with another row of short spines parallel with the anterior border, the last leg without this row of spines. Inner border of the dactylus, with 4-5 spinules, getting longer toward the end.
First pleopod of the male with its distal end hook-like, its base hairy. Abdomen triangular, the third to fifth segments fused; telson rounded distally. Abdomen of the female rounded. Carapace length of the male 24 mm, breadth 21 mm; of the female, length 26 mm, breadth 23 mm. (Dai & Yang, 1991)

Type locality: East Indies.
Range: Red Sea; Zanzibar (Lenz, 1905); Dar es Salaam (Hartnoll, 1975); South Africa - Cape of Good Hope (Ortmann, 1894a), Scottburgh, Isipingo, Durban, and Port St. Johns (Barnard, 1950); Mayotte Islands (Crosnier, 1965); Madagascar - Nosy Bé, Iles Glorieuses, Tuléar, and Ile Europa (Crosnier, 1965); Aldabra Islands (Lenz, 1905); Seychelles; Coëtivy Islands; Mauritius (Bouvier, 1915b, Michel, 1964)); Laccadive Islands (Alcock 1900); Sri Lanka (Alcock 1900); Andaman Islands (Alcock 1900); Sumatra - Aceh; Japan - Ogasawara-shoto (Stimpson, 1907), Shimoda (Sakai, 1935), Tateyama Bay, Manazuru, Shimoda, Kii Peninsula, Tosa Bay, Kagoshima Bay, Nagasaki and Northern Daito-jima (Sakai, 1939), Hachijo-jima (Sakai, 1954), Sagami Bay (Sakai, 1965b), from coast of Boso Peninsula to Okinawa, Hachijo-jima, Ogasawara-shoto and N. and S. Daito-jima (Sakai, 1976a), Kushimoto (Miyake, 1983), Ginowan, Okinawa (Shokita et al., 2000); Taiwan - T'ai-nan (Sakai, 1939), Chi-lung and T'ai-nan (Lin, 1949); China - Paracel Island (Chen, 1975), Hainan Island and Paracel Islands (Dai & Yang, 1991); Indonesia - Ambon (de Man, 1888d), Lombok, Sumbawa, Savu, Siau Island, Great Sangir Island, Karakelong Island, Kepulauan Talaud, and Atjatuning, west coast of New Guinea (Tesch, 1918a); Papua New Guinea - Kaiser Wilhelms-Land (Ortmann, 1894a), Nissan Island (Sendler, 1923); Palau (Sendler, 1923); New Caledonia - Poum (Takeda & Nunomura, 1976); Samoa - Tutuila and Upolu (Dana, 1852), American Samoa (Edmondson, 1959); Hawaiian Islands - Maui (Dana, 1852), Hawaii, Maui, Honolulu, and Kauai (Rathbun, 1906), Oahu (Edmondson, 1959); Line Islands - Palmyra and Tabuaeran (Edmondson, 1923, 1959); Marquesas Islands (Edmondson, 1959); Tahiti (Dana, 1852); Tuamotu Archipelago - Raraka (Dana, 1852).

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