Gecarcinidae, MacLeay, 1838

GUINOT, DANIÈLE, TAVARES, MARCOS & CASTRO, PETER, 2013, Significance of the sexual openings and supplementary structures on the phylogeny of brachyuran crabs (Crustacea, Decapoda, Brachyura), with new nomina for higher-ranked podotreme taxa, Zootaxa 3665 (1), pp. 1-414 : 109-110

Family Gecarcinidae

The male gonopore is sternal. Its position on sternite 8 varies within the family as presently diagnosed ( Ng & Guinot 2001; Ng, Guinot & Davie 2008). Sternite 7 is much expanded posteriorly in all genera. In Cardisoma ( Fig. 23A ; Guinot 1979a: fig. 54 A, B), the gonopore is very close to the P5 coxa and the membrane that lines its arthrodial cavity. In C. carnifex , the penis emerges just at the origin of suture 7/8, above the P5 coxo-sternal condyle. The narrow, proximal portion of the penis, which is concealed under the setae of the abdominal margin, joins the articular membrane of the P5 coxa and is wedged in a narrow space between the P5 coxo-sternal condyle and episternite 7. This portion is followed by a thick, sclerotised sheath (hard, punctate, and setiferous in C. carnifex ) and ends in a large, contorted papilla. Sternite 8 is practically completely covered by the abdomen. The penis does not seem capable of invagination, at least in the material examined.

In contrast, Gecarcinus H. Milne Edwards, 1837 (see Guinot 1979a: fig. 54D; Guinot & Bouchard 1998: fig.

25 A; N.K. Ng, Davie, Schubart & Ng 2007: 246, fig. 4H), Gecarcoidea H. Milne Edwards, 1837 , and Epigrapsus Heller, 1862 , have sternites 7 and 8 joined for a rather long distance so that the large gonopore is displaced farther from the P5 coxa and coxo-sternal condyle. The penis has a narrow, sclerotised portion along its inferior margin, and ends in a foliaceous papilla. The penis may invaginate, perhaps in the same way as in Varuna ( Fig. 36 ). In Gecarcinus and Gecarcoidea , the gonopore opens just below suture 7/8, and sternite 8 is not exposed (tufts of setae covering the genital region). In In the rather unusual gecarcinid Epigrapsus (see Liu & Jeng 2005: 135), the gonopore is far from suture 7/8, and a minute portion of sternite 8 is dorsally visible (the region lacks setae). This supports the views of Tavares (1989), who separated Gecarcinidae in at least two groups, one with Cardisoma and Discoplax , a second with Gecarcinus and Gecarcoidea . Epigrapsus seems closer to the second group. Cuesta, Liu & Schubart (2002), based on larval morphology, distinguished two major groups, one with Epigrapsus , Gecarcinus and Gecarcoidea , the second with Cardisoma . The disposition in Epigrapsus is different from that in Varuna ( Fig. 36 ), where there is a narrow episternite 7 joining the P5 coxo-sternal condyle, and a wide, largely exposed sternite 8 with an incomplete sulcus.

Concerning the proximity of the male gonopore to the P5 coxa, the condition in Cardisoma and Discoplax resembles that found in Grapsidae (at least Grapsinae MacLeay, 1838 ), which supports Tavares (1990), who regarded Gecarcinidae and Grapsidae as close. These two families were placed together in Grapsoidea by Ng, Guinot & Davie (2008: 214). Grapsus ( Fig. 23D ; Guinot 1979a: fig. 52 A; Karasawa & Kato 2001: fig. 2.19; N.K. Ng, Davie, Schubart & Ng 2007: fig. 4D) differs from Cardisoma and Discoplax in having a penis that is not basally wedged above the P5 coxo-sternal condyle and which is far from suture 7/8. Whereas the episternite 7 is relatively far from the male gonopore (and P5 coxo-sternal condyle) in Grapsus , episternite 7 joins the gonopore without a constriction at this level in Planes minutus ( Guinot 1979a: fig. 52C). In Planes , at least in the material examined, the complete penis is practically soft, with only a minute, hardly visible, sclerotised basal portion.

Based on overall similarities of zoeal morphology, Cuesta, Liu & Schubart (2002) and Cuesta & Anger (2005) suggested affinities of the group, including Gecarcinus , Gecarcoidea , and Epigrapsus , with Varunidae . According to these authors, Cardisoma and Discoplax share with the Sesarmidae antennal and abdominal morphologies, as well as the setation pattern of the maxillar endopodite. Schubart (2009: fig. 1) discussed the suitability of the diverse phylogenetic markers (16S rDNA sequences and nuclear copies) in comparing the American and West African representatives of Cardisoma as models. The phylogenetic status of Gecarcinidae and its relationships with the other thoracotremes remain unresolved as shown by molecular data ( Schubart & Cuesta 2010: 295, figs. 1, 2).

Figures

FIGURE 23. Sternal male gonopores in Thoracotremata. A, Cardisoma carnifex (Herbst, 1796) (Gecarcinidae), male, Madagascar (MNHN-B29589); B, Plagusia depressa (Fabricius, 1775) (Plagusiidae), male 40.0 × 44.0 mm, Senegal (MNHN- B11693): schematic view (see Fig. 33A) (abdomen indicated by dotted line); C, Ucides cordatus (Linnaeus, 1763) (Ucididae), male 70.0 × 93.0 mm, Brazil (MNHN-B13237) (abdomen indicated by dotted line); D, Grapsus grapsus (Linnaeus, 1758) (Grapsidae), male 57.0 × 60.0 mm, Clipperton I. (MNHN-B11538): schematic representation after dissection; E, F, Ocypode cursor (Linnaeus, 1758) (Ocypodidae), male 38.0 × 49.0 m, Senegal (MNHN): E, before dissection along dotted line; F, after dissection showing ejaculatory duct perforating somite 8, instead of P5 coxa. c, P5 coxo-sternal condyle; cx5, P5 coxa; e.d., ejaculatory duct; e7, episternite 7; g, gonopore; p, penis; p5, pereopod 5; 7, 8, sternites 7, 8; 7/8, thoracic sternal suture 7/8.

FIGURE 36. Sternal penis protection in Varunidae. Varuna litterata (Fabricius, 1798), male 41.2 × 46.0 mm, New Caledonia (MNHN-B-22720): penis emerging from large orifice on thoracic sternite 8. A, invaginated papilla; B, extended papilla. o, sclerotised sheath acting as an operculum; pa, papilla. Scale bar: 1 mm.