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(Adams & White, 1849)

Carapace oval, regions poorly defined, grooves separating epigastric discernible but shallow; gastric grooves separating cardiac and gastric regions very shallow, indistinct; most of dorsal surfaces very smooth and glabrous; frontal region narrow, slightly to distinctly rugose. Front short, gently sinuous, median part strongly deflexed downwards; lateral part of margin distinctly bilobed, forming distinct laterofrontal cleft. Supra- and infraorbital margins entire, smooth. Orbits oval (broader than long) or almost round. Antero-lateral margin strongly convex, clearly demarcated from gently convex, distinctly converging postero-lateral margin; external orbital tooth very low, rounded, but separated from rest of margin by distinct groove; rest of margin with three broad, convex lobes, separated from each other by small, shallow notches. Posterior margin of carapace gently sinuous. Antennules folding almost transversely, antennular fossae rectangular. Antennal flagellum well developed, basal segment stout, itself and subsequent two segments (excluding antennal peduncle) not entering narrow orbital hiatus, with third segment lodged in laterofrontal cleft of frontal margin. Anterior part of epistome clearly demarcated from posterior part, with median part distinctly sunken in; posterior martin with sharp triangular median structure. Endostome with low but distinct longitudinal ridge on each side. Outer surfaces of third maxilliped; ischium rectangular, median oblique sulcus distinct but shallow; merus quadrate; carpus rounded, subpediform; exopod stout, reaching anterior edge of merus, with rounded subdistal tooth on inner margin, flagellum long.
Ambulatory legs short, surfaces smooth, unarmed. Fourth ambulatory leg very short; propodus flattened, with straight or uneven ventral margin and scattered short stiff hairs on distal margins; propodus cylindrical, lined with numerous short and stiff hairs which partially obscures margins of proximal three-quarters, tip relatively sharp, corneous, distinctly turned upwards.
Chelipeds distinctly asymmetrical, right larger; outer surfaces of merus, carpus and chelae smooth; carpus short, rounded, inner distal angle with distinct low, rounded tooth; fingers shorter or subequal to palm, pigmented dark brown, quickly appearing greyish in preservative; larger cheliped with pronounced submolariform basal cutting tooth on cutting edge of dactylus and rounded teeth on proximal part of cutting edges of both fingers; cutting edges of smaller cheliped with numerous teeth and denticles.
Sternum broad, surface smooth; suture between sternites 1 and 2 absent; suture between sternites 2 and 3 distinct, deep; suture between sternites 3 and 4 marginal only, medially interrupted; sternite 4 broad; sternite 8 completely covered by last male abdominal segment. Male gonopore coxal.
Abdomen with 7-segmented, all segments freely movable; segments 3-5 trapezoidal, segment 6 rectangular, lateral margins gently concave; segment 7 triangular with gently convex lateral margins.
G1 long, slender, sinuous, distal part armed with short spines, tip slightly to distinctly flared, appearing triangular. G2 short, slender, distal part with petaloid process, no distal segment. (Ng & Wang, 1994)

Type locality: Eastern Seas.
Range: Red Sea (Nobili, 1906b, Klunzinger, 1913, Guinot, 1964b); Gulf of Aden - (Ng & Wang, 1994), Djibouti (Guinot, 1962a); Kenya - Mombasa; Tanzania - Dar es Salaam (Ortmann, 1894); South Africa - Port St. Jones (Barnard, 1950); Mayotte (Guinot, 1958); Iles Glorieuses; Juan de Nova; Madagascar - Fort-Dauphin; Seychelles - Coëtivy Islands (Rathbun, 1911); Mauritius (Richters, 1880, Michel, 1964); Pakistan - Makran coast (Alcock, 1898); Laccadive Islands (Alcock, 1898); Maldives (Guinot, 1962b); Chagos Archipelago - (Ward, 1942b), Diego Garcia (Rathbun, 1911); Andaman Islands (Alcock, 1898); Cocos-Keeling Islands (Ng & Wang, 1994); Christmas Island; Japan - Ogasawara-shoto (Stimpson, 1858a, 1907, Sakai, 1976a); Taiwan (Ng & Wang, 1994); China - Paracel Islands (Dai & Yang, 1991); Philippines; Palau (Takeda & Hayashi, 1973); Caroline Islands; Wake Island (Dana, 1852); Marshall Islands - Jaluit (Ng & Wang, 1994); Samoa (Alcock, 1898); Hawaiian Islands (Rathbun, 1906); Line Islands - Palmyra and Tabuaeran (Edmondson, 1923); Tuamotu Archipelago - (Dana, 1852), Makatea (Sendler, 1923).

Pseudozius caystrus