Gecarcinus nobilii, Perger, Robert & Wall, Adam, 2014

Perger, Robert & Wall, Adam, 2014, The description of a new species of the Neotropical land crab genus Gecarcinus Leach, 1814 (Crustacea, Decapoda, Brachyura, Gecarcinidae), ZooKeys 435, pp. 93-109 : 96-105

Taxon classification Animalia Decapoda Gecarcinidae

Gecarcinus nobilii sp. n. Figs 2 C–E; 3; 4; 5D

Gecarcinus ruricola . - Nobili 1901: 46.

Gecarcinus (Gecarcinus) lateralis quadratus . - Türkay 1970: 338. - Prahl and Manjarres 1984: 155.

Gecarcinus lateralis . - Türkay 1987: 147, fig. 7.

Material examined.

Holotype: male, carapace width (CW) 31 mm, Ecuador, Punta Galera, 0°50'N, 80°6'W, shore, collected near a pile of fairly fresh cow manure, Te Vega Expeditions, Sta. NO. XVIII-6, 22 April 1968. Coll. E. Ball (LACM CR 1968-477). Paratypes: 1 male, CW 26 mm, same location data as holotype (LACM CR 1968-478); 1 female, Ecuador, St. Elena (MNHN- B12314); 3 females, CW 28, 23, 23.5 mm, Ecuador, Esmeraldas (NHMB-NMB1010b). (Note: The female paratype (MNHN-B12314) (Fig. 3 D–F) of Gecarcinus nobilii sp. n. was labeled as "Gecarcinus festae Nobili/(co-type)/St. Helena/Festa/Museum Paris/Ecuador/Nobili 1901" without information about the label author. Nobili never published a description of a species by this name. In 1901 he described Sesarma festae and Uca festae and in the same contribution referred to specimens of Gecarcinus collected in Ecuador as Gecarcinus ruricola , which is restricted to West Atlantic Islands ( Türkay 1970; Bright and Hogue 1972).

Additionally, high resolution photographs of 14 captive individuals with unknown origin and 17 individuals taken at the following locations (confirmed by the photographers): Gorgona Island (Colombia) (Fig. 4 A–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), were examined.

Comparative material.

Gecarcinus lateralis (Freminville, 1835): lectotype male, CW 47.2 mm, Guadeloupe, M. Beaupertius leg. (MNHN-3758). Paralectotypes: 1 male, CW 50 mm, Guadeloupe, M. Beaupertius leg. (MNHN-3757); 1 female, CW 28 mm, same data as preceding specimen. 1 male, CW 32 mm, Martinique, M. Bellanger leg. (MNHN-3756); 1 female, CW 37 mm, Martinique, Bellanger leg., 24.09.1964 (MNHN-3755). Gecarcinus quadratus Saussure, 1853: syntype male, CW 39.7 mm, Mexico, Mazatlan (ANSP-CA3741). Pacific Gecarcinus lateralis (sensu Türkay 1973): 1 male, Mexico, Sinaloa, Estero el Verde (MNHN-B20900). 1 male, Costa Rica, Guanacaste, Playa del Coco, 5.8.1967, W. McCaul leg. (MZUCR13-01). 1 male, 1 female, Costa Rica, Puntarenas, Parque Nacional Manuel Antonio, 4.2.1995, J. Cortés leg. (MZUCR-2016). 1 male, Panama, Canas Island, Los Santos, Turtle Hatchery on S Beach, J. Frazier leg. (USNM-190711). Additional comparative material is cited in Table 1.

Derivation of specific epithet.

The species is named in honor of Giuseppe Nobili, who provided important contributions on the knowledge of crustaceans and built the crustacean collection in the Turin Museum (Italy). The species name is a noun in the genitive case.

Diagnosis.

Frontal width distinctly wider than the distance between the mesial ends of the suborbital cristae (Figs 2C; 3B, E). 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, E). Light lateral margin on dorsal carapace without lighter anterolateral and posterior patches (Figs 4C; 5D); cheliped carpus and palm homogeneously red or white (Fig. 4).

Description.

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 sub rectangular in cross-section; lateral margins subparallel, lined with low, obtuse spines and separate, short setae (Fig. 3 A–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. 3 A–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).

Geographic distribution.

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. 4 A–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.

Remarks.

The resemblance of the general habitus, the shape and the surface structure of carapace, chelipeds, ambulatory legs (Figs 3; 6-8) and the first male gonopod (Fig. 2E, F) indicate a close relationship between all mainland Gecarcinus populations. However, the trans-isthmian populations of Gecarcinus lateralis differ from Gecarcinus nobilii sp. n. by having a carapace front approximately as wide as the distance between the mesial ends of the suborbital cristae, and the width of the mesial lobe of the infraorbital margin at the point of contact with the carapace front is shorter than the shortest distance between the carapace front and the mesial end of the suborbital crista (Figs 2B; 6B, E; 7A, B).

A character commonly used to distinguish between species of the Gecarcinidae is the shape of the third maxilliped merus margin (e.g. Rathbun 1918; Türkay 1970; Perger et al. 2011). According to Rathbun (1918), the Atlantic population of Gecarcinus lateralis has an emarginated margin and the Pacific population a continuous margin. However, Bott (1955) and Türkay (1970, 1973) recognized the presence of both character states in trans-isthmian populations from Central America, South America and the Antilles, which we also observed in our sample from Central America. In contrast, all examined specimens of Gecarcinus nobilii sp. n. have a relatively continuous third maxilliped margin.

In addition to observed differences in morphological structures, the body color of Pacific Gecarcinus lateralis (sensu Türkay 1973) differs from Gecarcinus nobilii sp. n. in the following manner: Dorsal carapace without light lateral margin (Fig. 5A), dark dorsal carapace pattern extending laterally over anterolateral carapace border (Fig. 7E, F); orange patch at anterolateral and posterior carapace border (Figs 5A; 8G, H). Cheliped carpus and palm violet, rarely purplish (Fig. 8G, H). Atlantic Gecarcinus lateralis are distinguished from Gecarcinus nobilii sp. n. by following color differences: Light lateral margin on dorsal carapace with lighter (yellow to orange) patch at anterolateral and posterior carapace border (Figs 5B; 8A, B) or margin and anterolateral patch absent (Figs 5C; 8 D–F). Ventrolateral carapace color heterogeneous (Fig. 7 A–C). Cheliped carpus and palm heterogeneously purple, red, orange and/or whitish (Fig. 8 A–F).

Apart from the consistent color differences between Gecarcinus nobilii sp. n. and the other mainland populations of Gecarcinus , which provided the starting point for this contribution, the color differences between the trans-isthmian populations of Gecarcinus (Table 2; Figs 5 A–C; 7; 8) also drew our attention. According to Bright (1966), Gecarcinus from the Pacific coast of Central America has a brownish-red carapace and chelipeds with a purple tinge, while Gecarcinus lateralis from the Atlantic coast of Central America has a dark red carapace pattern and reddish-gray chelipeds. Chace and Hobbs (1969) provided the first color description of Gecarcinus lateralis from the West Indies, which widely agreed with the brief description of the Gecarcinus specimens from the Pacific coast of Central America by Bright (1966). Martinez and Bliss (1989) later described and illustrated the color of Gecarcinus lateralis from Bermuda and Bimini Islands in detail. The authors observed a remarkable variability in color and even color changes in single individuals, leaving open the possibility that Pacific Gecarcinus lateralis might also approach the range of variability observed in Atlantic Gecarcinus lateralis .

While the color of examined Gecarcinus lateralis from the Atlantic coast (n= 362) varied within the range described by Martinez and Bliss (1989) (see Fig. 8 A–F), the color of individuals of Pacific Gecarcinus lateralis examined in this study (n= 316) showed little variation (Fig. 8G, H) and did not approach the range of variability found in Gecarcinus lateralis from the Atlantic coast of Central America (Table 2) and Bermuda and Bimini Islands (see Martinez and Bliss 1989). In a sample totaling 678 individuals, only a single female from the Atlantic coast (Fig. 7D) did not clearly match with each of the color characters attributed to either the Atlantic and Pacific population (Table 2). This individual had a dark dorsal carapace color expanding laterally over the dorsolateral carapace border and sharply contrasting with the ventrolateral carapace color. However, the remaining characters (Table 2) agreed with the other individuals of Atlantic Gecarcinus lateralis . Within several groups of decapod crustaceans, color and color pattern reliably distinguish a number of species that differ little in morphology (e.g. Bruce 1975; Knowlton 1986). Color pattern-level and genetic differentiation between cryptic species has been observed in hermit crabs (e.g. Malay and Paulay 2009), spiny lobsters ( Ravago and Juinio-Menez 2003), porcelain crabs ( Hiller et al. 2006) and in the Gecarcinidae genus Discoplax A. Milne-Edwards, 1867 ( Ng and Davie 2012).

Studies of genetic divergence and reproductive isolation are needed to evaluate whether Gecarcinus quadratus should be retained as a synonym of Gecarcinus lateralis , or alternatively, the trans-isthmian populations of Gecarcinus lateralis represent allopatric sister species.

Evolutionary relationships.

When we consider the closure of the Panamanian Isthmus as a calibration point for morphological divergence between the trans-isthmian populations of Gecarcinus lateralis , the virtual lack of morphological differentiation (other than color) between them and the distinctness of Gecarcinus nobilii sp. n. suggests that Gecarcinus nobilii sp. n. evolved from a common ancestor before the Isthmus closed. The common ancestor of the trans-isthmian Gecarcinus lateralis may have been restricted to North America and/or the emerging Isthmus, which is assumed to have been a peninsula of North America ( Kirby et al. 2008), and the ancestor of Gecarcinus nobilii sp. n. to South America. Nevertheless, the distribution of the gecarcinid Johngarthia planata Stimpson, 1860, from Gorgona Island to Mexico (reviewed by Perger et al. 2013) and Cardisoma crassum Smith, 1870, from Peru to Mexico ( Türkay 1970) as well as the absence of Gecarcinus nobilii sp. n. from the Atlantic coast of South America suggests a more complex pattern. A promising approach to further investigation of the speciation processes in Neotropical Gecarcinidae may be the evaluation of how the connection between the habitats of the adults via sea currents may have changed during the formation of the Isthmus (see Schneider and Schmittner 2006; Molnar 2008). Further studies should also take into account that even today, as indicated by the actual distribution, there appear to be mechanisms separating the Gecarcinus populations from the Central and South American Pacific coast.