Megalobrachium mortenseni Haig, 1962

(Fig. 1 A)

Megalobrachium mortenseni Haig, 1962: 189, figures 2–5 (type-locality: Virgin Islands, northwest of St. John, west of Congo Cay).

Material examined. Brazil: Bahia—Abrolhos, 1 female (MZUSP-10652); Recife de Popa Verde, 3 males, 1 female (MNRJ-6782). Espírito Santo – Piúma, 20°50’578”S, 40°28’553”W, 21.5 m, 3 males, 1 ovigerous female (MZUSP-24529). Rio de Janeiro—Ilha Grande, Praia do Furão, 1 male (MNRJ-3646); Cabo Frio, Búzios, Praia da Armação, 1 male (MNRJ-3816). São Paulo—São Sebastião, Praia do Porto, 1 ovigerous female (MZUSP-9531).

Recognition characters. Carapace rounded, as long as broad in males, slightly broader than long in females; quite eroded; lateral margins with crenulate crest; protogastric ridge and cervical groove evident; gastric region elevated, posterolateral region plicated. Pterygostomial flap of carapace with median longitudinal serrate crest. Front with serrate margin. Chelipeds equal, eroded and covered with small rounded tubercles; merus rugose, with small, serrate distal lobe on flexor margin; carpus with 4 longitudinal crenulate carinae, small lobe in proximal third on flexor margin; propodus with 3 longitudinal crenulate carinae; dactylus with 1 longitudinal crenulate carina. Walking legs slender, carpus with 2 serrate crests on extensor margin; propodus with 5 spines on flexor margin, dactylus with 4 spines on flexor margin. Gonopods present in males. Telson composed of 7 plates.

Habitat. Intertidal region down to depths of 30 meters, usually on rocky substrates.

Geographic distribution. Western Atlantic—Honduras, Roatán, Bay Islands; Panama, Bocas del Toro and Limón Bay; Virgin Islands, St. John; Colombia, Santa Marta and Rosario Islands; Venezuela, Margarita Island; and Brazil (Pará to São Paulo).