Polyonyx gibbesi Haig, 1956

(Fig. 3 B)

Porcellana macrocheles Gibbes, 1850: 191; 1854: 6, pl. 1, fig. 5 [non Porcellana macrocheles Poeppig, 1836]. Polyonyx macrocheles— Stimpson, 1858: 229.

Polyonyx gibbesi— Haig, 1956: 28 (type-locality: South Carolina, USA).

Material examined. Brazil: Rio de Janeiro—Angra dos Reis, 5 males, 2 females, 6 ovigerous females (MNRJ- 3787). São Paulo—São Sebastião, Praia do Araçá, 2 males, 2 females, 2 ovigerous females (MZUSP-6962). Paraná—Saco do Limoeiro, 1 ovigerous female (MZUSP-12763). No locality— 1 male, 1 ovigerous female (MZUSP-7146).

Recognition characters. Carapace subrectangular, about 3 times broader than long; smooth, except for discrete rugae on posterolateral margin; strongly convex; epibranchial angle well-produced. Front with straight margin. Chelipeds subequal, subcylindrical; propodus twisted, compressed, more evident on minor cheliped, fringed with long setae on extensor margin; fingers short, grooved and crenulate on cutting face. Walking legs smooth, compressed, pubescent; ischium with row of distal spinules on flexor margin; propodus with row of 3 spines on flexor margin, dactylus short, ending in a curved, two spines claw, flexor margin with 2 spines, smaller than terminal claw. Gonopods present in males. Telson composed of 7 plates.

Habitat. A common commensal of polychaetes, living in pairs and, rarely, found outside their tubes. From the intertidal zone down to depths of 47 m (Williams 1984), on rocks, sand and mud from sublittoral region (Veloso 1999).

Geographic distribution. Western Atlantic—USA, Massachusetts, Rhode Island, North and South Carolina, eastern and western Florida, Texas; Panama, Caledonia Bay; Cuba; Puerto Rico; Trinidad; Venezuela, Punta Papuy; Brazil (from Ceará to Rio Grande do Sul); Uruguay, La Paloma; and Argentina, Mar del Plata.

Remarks. According to Rodríguez et al. (2005), Polyonyx gibbesi is the only species of the genus that occurs in the western Atlantic.