Chasmocarcinus meloi Coelho & Coelho 1998
Creators: name: Ng, Peter K. L.
name: Castro, Peter
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Chasmocarcinidae
Chasmocarcinus
Chasmocarcinus meloi

description: Chasmocarcinus meloi Coelho & Coelho, 1998
(Figs. 4 G; 22D; 29G; 37A, B; 50E; 65J)
Chasmocarcinus sp. A.—Barreto et aI. 1991: 291 [in list]; 1993: 651 [in list].
Chasmocarcinus meloi Coelho & Coelho, 1998: 805, 809, 813, figs. 8, 9 [type localilty: Brazil, Algoas].— Coelho et al. 2008: 12 [in list].— Ng et al. 2008: 76 [in list].
Type material (not examined). Holotype male (DOUFPE 503), Brazil, Algoas, Akaroa, stn 170, 10°33.7'S, 36°16.5'W, 50 m, 0 3.12.1965.
Paratypes: 2 males (MZUSP 13606, ex-DOUFPE 508; see Melo et al. 2003: 431), Akaroa, stn 181, 10°38.15’S, 36°17.2'W; 5 females (DOUFPE 500, DOUFPE 501, DOUFPE 505, DOUFPE 506, DOUFPE 509), type locality; 1 male (DOUFPE 507), type locality, specimen of unknown sex (DOUFPE 504), type locality..
Diagnosis. Anterolateral margins of carapace (Fig. 4 G; Coelho & Coelho 1998: fig. 8a) with conspicuous granular ridge. Front straight or slightly bilobed. Orbits short, proportionally short eye peduncles (Fig. 22 D; Coelho & Coelho 1998: fig. 8b). Epistome (Fig. 22 D) with semicircular median lobe with median fissure, lateral margins straight. Antennular articles relatively short (Fig. 21 D). Third maxilliped (Fig. 29 G; Coelho & Coelho 1998: fig. 8c) ischium rectangular, slightly longer than ovate merus. Bulging pterygostomial region, clearly visible from dorsal view. Fingers of major chela of holotype male (Fig. 37 A; Coelho & Coelho 1998: figs. 8e, 9a) proportionally short, slightly shorter than propodus in dorsal view; pollex as long as dactylus; small teeth of similar size along cutting margins. Fingers of minor chela of holotype male (Fig. 37 B; Coelho & Coelho 1998: figs. 8e, 9a) scissor-like; with small, sharp teeth. Outer surface of carpus of major chela of males sometimes eroded. Inner margin of cheliped carpus smooth (Fig. 4 G; Coelho & Coelho 1998: fig. 8 a, b). Ambulatory legs (Fig. 4 G; Coelho & Coelho 1998: fig. 8a, d) proportionally short, folded P5 merus only reaching middle portion of anterolateral margin; no subdistal spur on P5 dactylus. Fused thoracic sternites 1, 2 broadly triangular, proportionally narrow, short. Male pleon (Fig. 50 E; Coelho & Coelho 1998: fig. 9d) with proportionally short, wide telson. G1 medium size, slightly stout, spinules along distal half (Fig. 65 J; Coelho & Coelho 1998: fig. 9e). G2, female pleon, thorax, vulvae undescribed.
Remarks. Coelho & Coelho (1998) described C. meloi as a new species primarily on a single diagnostic character: a straight, distinctly non-bilobed front. This character, however, is not reliable because the relative shape of the front varies depending on how the carapace is viewed. The series of specimens of C. arcuatus examined, the closest species to C. meloi, possess frontal margins that vary from prominently bilobed (Fig. 2 E, F) to slightly bilobed (Fig. 2 G), even if they are viewed the same way, and we are of the opinion this character is not a useful species-specific one.
Chasmocarcinus arcuatus was described as a distinct Brazilian species on account of the arched, curved fingers of the major chela of large males. In these large males, the gap between the arched fingers is wide and the pollex is armed with two teeth (Coelho & Coelho 1998: figs. 1a, 2c), the outer surface of the propodus of the major chela is eroded (Coelho & Coelho 1998: fig. 3 c–e), and the inner surface setose. The arching of the fingers was found to vary with overall size, with smaller males possessing more typical chelae (Coelho & Coelho 1998: 813) (see Fig. 35 G, H). Chasmocarcinus meloi, however, never has arched fingers, even in the larger specimens reported by Coelho & Coelho (1998: fig. 8a, e, 9a), and as noted above, its frontal margin is almost entire.
We are not convinced the two species are different. All the remaining characters used to distinguish between the Brazilian species of Chasmocarcinus (absence of a tooth on the inner margin of the cheliped carpus; absence of a suborbital ridge; morphology of the carapace, third maxillipeds, and G1; and relative length of the ambulatory legs) are shared by both C. arcuatus and C. meloi. Significantly, their carapace shapes are also very similar, both species possessing a more quadrate carapace in which the anterolateral margins are more angular (Coelho & Coelho 1998: 802, 809). In the present series of specimens we identify with C. arcuatus, the carapace of the largest male is slightly less quadrate (Fig. 2 E) but in smaller males and females the carapaces are clearly quadrate (Fig. 2 G, H). The cheliped fingers of the material identified as C. meloi by Coelho & Coelho (1998) could well be C. arcuatus, with the specimens not having arched cheliped fingers, a condition shown in some specimens of C. arcuatus males by Coelho & Coelho (1998: fig. 3a, b). Of interest is that Coelho & Coelho (1998: 803) noted that the outer surface of the chela was “eroded”, and we see the same condition in the smaller males of C. arcuatus examined here (Fig. 35 G, H), even though the fingers are not arched as yet. Although Coelho & Coelho (1998) noted the unique morphology of the major chela of C. arcuatus, they did not take into account the possibility that differences between the chelae of C. arcuatus and C. meloi could have been due to regrowth of chelae after loss. The G1 of C. meloi (Fig. 65 J; Coelho & Coelho 1998: fig. 9e), a much more reliable character, is very similar, if not identical, to that of C. arcuatus (Fig. 63 D, E, G, H). If the cheliped and frontal margin differences are part of variation, then C. arcuatus and C. meloi cannot be separate species. We have nevertheless not taken any formal action to synonymise the two species since we have only limited material of both species, and more importantly, not seen the types. This will have to be confirmed in more detailed studies of the two species.
Distribution. Brazil (Maranhão to Bahia). Depth: 21‒ 130 m.
description: Published as part of Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), pp. 1-182 in Zootaxa 4209 (1) on pages 25-26, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646