Xanthoidea, 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 : 144-145

Superfamily Xanthoidea

The male gonopore is coxal. Xanthidae does not show a coxo-sternal condition, which is linked to a weak carcinistation (no posterior widening), and a small sternite 8 is only exposed in a few genera ( Guinot 1968a; 1979a: figs. 47A, 48; Lai et al. 2011: fig. 8g, h). In contrast, a coxo-sternal condition may be present in Panopeidae and Pseudorhombilidae .

The Panopeidae exhibits character mutistates from a coxal to a coxo-sternal condition, resulting in a characteristically long penis in Eucratopsinae ( Fig. 8J ; Guinot 1969a: 24). For example, Prionoplax spinicarpus exhibits an exceptionally long and completely concealed penis ( Figs. 8K , 14 ; see Modalities of penis protection: Coxo-sternal penial tube). The panopeid sternal pattern includes complete sutures 6/7 and 7/8 ( Fig. 56 ) but a variously developed median line, along sternites 6–8 in Panopeus africanus and P. chilensis H. Milne Edwards & Lucas, 1843 , sternites 4–8 in Eurypanopeus transversus (Stimpson, 1860) , and sternites 7, 8 in Rhithropanopeus harrisii (Gould, 1841) and Prionoplax spinicarpus (the three later with a small triangle at the suture 6/7 level). The peculiar disposition of Rhithropanopeus Rathbun, 1898 , was described by Bouvier (1940: 259, fig. 167, as Heteropanope tridentatus ).

The Pseudorhombilidae Alcock, 1900 , shows a tendency towards a coxo-sternal condition, with a fully developed protection in some species. Transitional patterns are observed in Pseudorhombilinae Alcock, 1900 , from a plesiomorphic condition in Bathyrhombila Hendrickx, 1998 ( Hendrickx 1998: fig. 2B), Chacellus Guinot, 1969 (Guinot 1969c: fig. 138), Euphrosynoplax Guinot, 1969 (Guinot 1969c: fig. 139), and Nanoplax Guinot, 1967 (considered primitive “catometopous stages” in Hendrickx 1998: 639) to a coxo-sternal condition in Pseudorhombila H. Milne Edwards, 1837 , Oediplax Rathbun, 1897 ( Hendrickx 1998: 641, 642), and Trapezioplax Guinot, 1969 (Guinot 1969c: fig. 142). According to Hendrickx (1998: 638), the condition varies within Pseudorhombila itself, depending on the degree of connection between sternites 7 and 8, which are not completely joined in P. xanthiformis Garth, 1940 ( Hendrickx 1995: fig. 1C) but completely joined in P. octodentata (Rathbun, 1906) (Guinot 1969c: 113; Hendrickx 1995: fig. 1A), P. quadridentata (Latreille, 1828) , and P. ometlanti Vázquez-Bader & Gracia, 1995 . P. quadridentata (Latreille, 1828) shows two marked triangles at the level of sutures 6/7 and 7/8, and a median line along sternites 7 and 8 corresponding to a high median plate, plus an anterior trace of median line corresponding to a corneous median plate. The pattern is similar in Oediplax granulata Rathbun, 1894 , and Chacellus filiformis Guinot, 1969 .

Speocarcinus shows a coxo-sternal condition similar to that of Pseudorhombilidae , with a short dorsal junction of sternites 7 and 8 (Guinot 1969c: fig. 120). The taxonomic status of Speocarcinus has been uncertain for a long (Guinot 1969c; Ng 1987a), with a previous inclusion in Goneplacidae ( Rathbun 1918; Melo 1996; Williams 1984; D'Incao & Silva 1991; Rieger et al. 2003), and then as the onomatophore (type genus) of Speocarcinidae Števčić, 2005 , erected within Xanthoidea ( Števčić 2005: 54) . The Speocarcininae Števčić, 2005 , considered a subfamily of Xanthidae ( Ng, Guinot & Davie 2008: 201, 208; De Grave et al. 2009: 43; Schweitzer et al. 2010: 127; Brandão et al. 2010, 2012; Lai et al. 2011), is transferred here to Pseudorhombilidae , see below. The large genus Speocarcinus as reviewed by Brandão et al. (2012: figs. 1 – 9) is probably polyphyletic as evidenced by the variation of the thoracic sternal sutures (sternites 4/5 to 7/8 apparently all incomplete, or suture 6/7 complete and suture 7/8 apparently varying; varying shape of the first sternites), the size and curvature of the G1s, and the location and orientation of the vulvae on sternite 6.

Ng, Guinot & Davie (2008) restricted Xanthoidea to three families, Xanthidae , Panopeidae and Pseudorhombilidae . A molecular phylogeny using five loci ( Thoma & Felder 2009) supported the monophyly of Xanthoidea but recovered a paraphyletic Xanthidae and, in addition, indicated the xanthid subfamilies as polyphyletic (see also Felder & Thoma 2010: fig. 5). A multi-gene approach by Lai et al. (2011) supported Panopeidae as a monophyletic group, suggesting that it was nested within the Xanthidae and should be recognised as a subfamily, i.e., Panopeinae Ortmann, 1893 , within Xanthidae . It also supported the assignment of Speocarcininae to Pseudorhombilidae , the more parsimonious hypothesis leading to recognise Pseudorhombilidae as a subfamily ( Pseudorhombilinae Alcock, 1900 ) within Xanthidae , Speocarcininae consequently becoming a junior synonym of Pseudorhombilinae . These results corroborated those of Thoma et al. (2009).

Figures

FIGURE 8. Coxal gonopore in heterotreme families, including families with coxo-sternal condition (D, G, I–K). A, Corystes cassivelaunus (Pennant, 1777) (Corystidae), male 33.0 × 26.0 mm, Bay of Biscay, (MNHN-B27912); B, Thia scutellata (Fabricius, 1793) (Thiidae Thiinae), male 17.7 × 19.0 mm, Mediterranean Sea (MNHN-B416); C, Xantho hydrophilus (Herbst, 1790) (Xanthidae Xanthinae), male 20.5 × 33.0 mm, France, Concarneau; D, Goneplax rhomboides (Linnaeus, 1758) (Goneplacidae Goneplacinae), male 12.0 × 21.0 mm, Tunisia (MNHN-B10159); E, Pilumnus hirtellus (Linnaeus, 1761) (Pilumnidae Pilumninae), male, Mediterranean Sea (MNHN); F, Menippe mercenaria (Say, 1818) (Menippidae), male, Florida (MNHN-B9500); G, Ommatocarcinus macgillivrayi White, 1851 (Goneplacidae Goneplacinae), male 27.7 × 73.6, Australia, New South Wales (MNHN-B10216); H, Bythograea thermydron Williams, 1980 (Bythograeidae), male 33.0 × 60.0 mm, paratype, Galapagos Rift (MNHN-B6468); I, Rhizopa gracilipes Stimpson, 1858 (Pilumnoidea Rhizopidae), male 6.3 × 8.8 mm, Thailand (MNHN-B24500); J, Malacoplax californiensis (Lockington, 1877) (Panopeidae), male 10.0 × 14.0 mm, Gulf of California (MNHN-B10212); K, Prionoplax spinicarpus H. Milne Edwards, 1852 (Panopeidae), male 14.8 × 22.2 mm, holotype, [? China: erroneous origin] (MNHN-B10347). In E, F, penis emerging from P5 coxo-sternal condyle. a1, a3, abdominal somites 1, 3; c, coxo-sternal condyle; cx5, P5 coxa; e7, episternite 7; g, gonopore; m.l., median line; p, penis; 7, 8, thoracic sternites 7, 8; 6/7, 7/8, thoracic sternal sutures 6/7, 7/8.

FIGURE 14. Derived coxo-sternal condition showing penis sheltered in gutter and location of “supplementary” suture 7/8 at complete dorsal junction of sternites 7 and 8 (both separated here to expose penis), “true” suture 7/8 situated below. Prionoplax ciliata Smith, 1870 (Panopeidae Eucratopsinae), male 13.4 × 20.3 mm, Panamá (MNHN-B24490). cx4, cx5, P4, P5 coxae; g, gutter; p, penis; pa, papilla; 7, 8, thoracic sternites 7, 8; 6/7, 7/8, thoracic sternal sutures 6/7, 7/8. Scale bar: 2 mm.

FIGURE 56. Diagrammatic representation of patterns of thoracic sternal sutures 4/5–7/8 and modalities of median line (median plate not taken into account) in Eubrachyura. A, pattern 1: sutures 4/5–7/8 complete (uninterrupted), median line along sternites 5–8, may extend on sternite 4; B, pattern 2: only suture 4/5 interrupted, median line along sternites 6–8; C, pattern 3: sutures 4/5, 5/6 interrupted, median line along sternites 7, 8; D, pattern 4: sutures 4/5–6/7 interrupted, median line on sternite 8; E, generalised pattern 5: sutures 4/5–7/8 incomplete, median line variable among subpatterns a-f; F, pattern 6: sutures 4/5–7/8 interrupted, suture 6/7 complete, median line along sternites 7, 8; G, subpattern 5a: sutures 4/5–7/8 interrupted, median line absent; H, subpattern 5b: sutures 4/5–7/8 interrupted, median line along sternites 3–8; I, subpattern 5c: sutures 4/5–7/8 interrupted, median line along sternites 5–8, sometimes partially on sternite 4; J, subpattern 5d: sutures 4/5–7/8 interrupted, median line along sternites 5–7; K, subpattern 5e: sutures 4/5–7/8 interrupted, median line along sternites 7, 8; L, subpattern 5f: sutures 4/5–7/8 interrupted, median line on sternite 4. Each thoracic sternum with same width; all sutures represented parallel, equidistant, and similar. Some additional patterns are not figured.