Gecarcinus nobilii Perger & Wall 2014

Gecarcinus nobili is a species of land crab closely related to the halloween moon crab (G. quadratus). It was described in 2014. It is from the Neotropical Pacific coast of northwestern South America.

Carapace transversely ovate, widest in anterior half, dorsal surface smooth. Cardiac, gastric and branchial chambers moderately swollen (Fig. 3B, E). Median groove distinct, cervical and urogastric grooves weakly developed; three relatively small pits anterior (close to orbit), median and posterior of cervical groove, one in urogastric groove (Fig. 3A). Supraorbital margin gently sinuous, with small granules, confluent with anterolateral margin; exorbital tooth weakly developed, tip not over-reaching orbit (Fig. 3B, D, E); granules along anterolateral and orbital margins weakly developed. Eyes well developed, filling orbital cavity; eyestalks short (Fig. 3B, E). Carapace front distinctly wider than the distance between mesial ends of the suborbital cristae (Figs 2C; 3B, E), deflexed downwards, concealing basal segments of antennules. Width of mesial lobe of infraorbital margin at point of contact with carapace front longer than shortest distance between carapace front and mesial end of suborbital crista (Figs 2C; 3B, D; 4H). Suborbital, pterygostomial regions sparsely granular laterally. Subhepatic region with rounded postero-lateral margins, with rows of small granules. Epistom linear, sunken. Third maxilliped merus and outer ventral orbital border furnished with long setae (Fig. 3D); third maxilliped merus enlarged, reaching mesial border of suborbital crista, triangular, apex straight or moderately convex (Figs 3B, 4I); exopodit short, not protruding beyond third maxilliped ischium-merus joint, without flagellum; palpus concealed by external border of third maxilliped merus. Chelipeds subequal; in large males larger with respect to the carapace width, surfaces relatively smooth, weakly granulate. Merus with transversal rows of small tubercles; dorsal margin rugose or with moderately developed, obtuse granules; ventral margin lined with weakly developed granules, otherwise smooth. Carpus with 2–5 well developed triangular inner subdistal tooth (Fig. 3A, B, E). Merus and carpus margins smooth in large individuals. Chela large, length not exceeding carapace width, surfaces smooth; lower margin gently sinuous. Fingers slightly shorter or as long as palm, tapering, gently curved, drop-shaped in cross-section, proximal half with irregular arranged pores and low, pectinated teeth; teeth on distal portion of finger arranged on well defined, subparallel longitudinal ridges, longitudinally separated by grooves with pores. Cutting margins with distinct triangular teeth along length; fingers without or with small gap between them when closed, ending in sharp, pectinated tips. Ambulatory legs with second pair longest, last pair shortest; surfaces smooth to slightly rugose. Merus dorso-laterally flattened, cross-section triangular, stout; with transversal rows of small tubercles, dorsal margin distinct, granulated, with separate, short setae. Carpus stout, subtriangular in cross-section; dorsal surface with three carinae, median carina distinct, serrated or granular; dorso-lateral carinae weakly developed or absent; margins and carinae lined with separate, short setae. Propodus subrectangular in cross-section; lateral margins subparallel, lined with low, obtuse spines and separate, short setae (Fig. 3A–C). Dactylus elongate, styliform, gently curving, subquadrate in cross-section, margins lined with distinct spines and separate, short setae; apical half of spines and dactylus tip corneous; lateral carina of dactylus weakly developed or absent (Fig. 3A–C). Male abdomen relatively broad (Fig. 3C), all abdominal somites and telson distinct, freely articulating. Somite 1 filling space between last pair of ambulatory legs, longitudinally very narrow. Shape of somite 2 similar to somite 1 but narrower. Somites 3–5 increasingly trapezoidal in shape, lateral margins relatively straight. Somite 6 longest, longer than telson, distinctly wider than long, with lateral margin strongly convex. Telson sub-triangular, narrowest abdominal segment; as long as wide, lateral margins gently concave to almost straight, tip rounded (Fig. 3C). First male gonopod with basal and terminal segment (Fig. 2E). Basal segment stout, straight, with digiform projection on distomesial end, projection directed in same manner with distal segment, fringed with long setae. Terminal segment about one-third of first gonopod (when seen from lateral view, Fig. 2E), folded longitudinally, compressed dorsoventrally, tapering and curved distally, slightly projecting over distal setae, laterally with narrow, longitudinal furrow. Sex independent color dimorphism: red and white males and females (Fig. 4). Both forms with dark median pattern and contrasting light lateral margin on dorsal carapace without lighter anterior and posterior patches (Fig. 5D), margin of same color as lateral carapace; dark dorsal carapace pattern with pointed anterolateral edges anteriorly reaching the orbits (Fig. 5D). Mesial lobe of infraorbital margin mostly grey (Fig. 4). Red form with red lateral margin on dorsal carapace. Carapace pits white to orange. Legs and chelipeds uniformly red, inner sides of fingers cream to white, margin of the third maxilliped merus, coxa, basis and ischium of chelipeds and ambulatory legs whitish. In white form, lateral margin on dorsal carapace orange/white or completely white. Ventral carapace and chelipeds white, legs and carapace pits light orange to white (Fig. 4).

Gecarcinus nobilii sp. n. is currently known to occur from Punta Galera and St. Elena (Ecuador). It is also documented in photographs taken at Gorgona Island (Colombia) (Fig. 4A–C), Chucheros Beach (Buenaventura, Colombia) (Fig. 4D), Canangucho Forest Reserve (Nuquí, Chocó, Colombia) (Fig. 4E), Ayampe (Manabí, Ecuador) (Fig. 4F), and Isla de la Plata (Ecuador). Individuals of Gecarcinus previously reported from Peru (Türkay 1970) may also refer to Gecarcinus nobilii sp. n. Available data and the photographs found during the Internet search suggest that Gecarcinus nobilii sp. n. replaces Pacific Gecarcinus lateralis between the Darien province (Panama) and the Choco dept. (Colombia). In addition to the individuals of Pacific Gecarcinus lateralis found during fieldwork (Table 1), the Internet search revealed numerous photographs of Pacific Gecarcinus lateralis from Central America. However, there are no photographs of Pacific Gecarcinus lateralis from within the distributional area of Gecarcinus nobilii sp. n.