Chasmocarcinus meloi Coelho & Coelho, 1998

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182: 25-26

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Chasmocarcinus meloi Coelho & Coelho, 1998


Chasmocarcinus meloi Coelho & Coelho, 1998 

( Figs. 4View FIGURE 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.GoogleMaps 

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. 4View FIGURE 4 G; Coelho & Coelho 1998: fig. 8a) with conspicuous granular ridge. Front straight or slightly bilobed. Orbits short, proportionally short eye peduncles ( Fig. 22View FIGURE 22 D; Coelho & Coelho 1998: fig. 8b). Epistome ( Fig. 22View FIGURE 22 D) with semicircular median lobe with median fissure, lateral margins straight. Antennular articles relatively short ( Fig. 21View FIGURE 21 D). Third maxilliped ( Fig. 29View FIGURE 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. 37View FIGURE 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. 37View FIGURE 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. 4View FIGURE 4 G; Coelho & Coelho 1998: fig. 8 a, b). Ambulatory legs ( Fig. 4View FIGURE 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. 50View FIGURE 50 E; Coelho & Coelho 1998: fig. 9d) with proportionally short, wide telson. G1 medium size, slightly stout, spinules along distal half ( Fig. 65View FIGURE 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. 2View FIGURE 2 E, F) to slightly bilobed ( Fig. 2View FIGURE 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. 35View FIGURE 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. 2View FIGURE 2 E) but in smaller males and females the carapaces are clearly quadrate ( Fig. 2View FIGURE 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. 35View FIGURE 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. 65View FIGURE 65 J; Coelho & Coelho 1998: fig. 9e), a much more reliable character, is very similar, if not identical, to that of C. arcuatus  ( Fig. 63View FIGURE 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.














Chasmocarcinus meloi Coelho & Coelho, 1998

Ng, Peter K. L. & Castro, Peter 2016

Chasmocarcinus meloi

Coelho & Coelho 1998: 805