Hymenosomatidae, McLeay, 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 : 125-126

Family Hymenosomatidae

The short penis emerges from a large gonopore, which opens on the slope of sternite 8 far from suture 7/8, one of the posteriormost locations on sternite 8 among the Brachyura ( Guinot 1979a: fig. 53F; Guinot & Richer de Forges 1997: figs. 6A, 9) (see Modalities of penis protection: “Sternitreme” protection). The distance between the gonopore and the P5 coxa varies among genera, from short as in the cavernicolous Cancrocaeca xenomorpha Ng, 1991 ( Fig. 29A ) to longer as in Odiomaris pilosus ( Fig. 29B ), as a consequence of the broadening of the thoracic sternum (see female sternum, Fig. 48C ). The gonopore is large, as in Limnopilos microrhynchus (Ng, 1995) ( Guinot & Richer de Forges 1997: 475) .

The position of the male gonopore of the hymenosomatids has been a source of confusion, partially due to the small size of individuals, so the taxonomy of these very peculiar crabs has undergone several major changes (see historical account or discussion by Gordon 1940; Melrose 1975; Guinot 1978a, 1979a; Lucas 1980; Rice 1980, 1981a; Feldmann & McLay 1993; Guinot & Richer de Forges 1997). H. Milne Edwards (1837a: 29, 33, 35) assigned Elamena H. Milne Edwards, 1837 , and Hymenosoma Desmarest, 1825 , to his tribe Pinnothériens in the Catometopa on the basis of sternal instead of coxal male gonopores. De Haan (1839: 75, pl. 29, fig. 1) referred to his Majacea “ Ocypode (Elamena) unguiformis ” called in his plates “ Inachus (Elamena) unguiformis ”, now Trigonoplax unguiformis (De Haan, 1839) . Henri Milne Edwards (1852: 103, 183) was in favour of a separate tribe, establishing a link between the Ocypodiens and the Homoliens, but also showing majids traits. Ortmann (1893: 30; 1896: 416, 441, 442) noted the sternal location of male gonopores, comparable to that of Leucosiidae , and chose, however, a placement in Majoidea , perhaps in an “aberrant” group. This was considered “a decided mistake” by Alcock (1900b: 282, 291, 385), who included Hymenosomatidae in the Catometopa. Despite the presence of sternal male gonopores, Rathbun (1925: 561) assigned the family to Majoidea .

Hymenosomatids have often been considered heterotremes, as a family of the Oxyrhyncha Latreille, 1802 ( Shen 1932: 41, 58; as Hymenosomidae ) or Majoidea , hence the common name of “false spider crabs” ( Ng, Guinot & Davie 2008: 108; De Grave et al. 2009: 35; Schweitzer et al. 2010: 93), or in its proximity ( Davie 2002: 342; Poore 2004: 390), or placed in a separate superfamily, Hymenosomatoidea ( Guinot 1978a: 284; Martin & Davis 2001: 74; Chen & Sun 2002: 34; Števčić 2005: 101). But they were also considered thoracotremes, often close to Pinnotheridae ( Haswell 1882; Miers 1886; Alcock 1900b; Garth 1958; Guinot 1978a; McLay 1988; Števčić 1998), even with the genera simply merged into this family ( Dana 1851a, 1852; Hodgson 1902; Hutton 1904; Baker 1906). Most often, their taxonomic position was not given or discussed ( Lucas 1980; Ng & Chuang 1996; Van den Brink 2006; Naruse & Ng 2007a; Naruse, Ng & Guinot 2008; Naruse, Mendoza & Ng 2008; Van den Brink & McLay 2009; McLay & Van den Brink 2009; Naruse & Komai 2009; Teske et al. 2009; Husana et al. 2011).

Tesch (1918: 3) clearly stated that the only character justifying a placement of Hymenosomatidae among the Catometopa was the sternal opening, this trait being “counterbalanced by a whole series of features showing a close relationship to the Oxyrhyncha and especially to the Maiidae”. The dilemma of whether or not there is a true sternal emergence of the male gonopores in hymenosomatids has been discussed by Montgomery (1921: 95) and briefly by Guinot (1979a: 215). According to Richer de Forges (1976, 1977), the Hymenosomatidae was related to Majidae , the sternal emergence of the male openings being considered deceptive. A coxo-sternal, thus heterotreme condition was assumed by Guinot & Richer de Forges (1997) and Guinot & Bouchard (1998) (see also Števčić 2005: 101), who proposed a close relationship between Hymenosomatidae and Inachoididae .

Several dissections demonstrated that the ejaculatory duct was directly connected with the testis instead of perforating the P5 coxa ( Fig. 58A, B ) and thus it was not a coxo-sternal condition. Moreover, the remarkably transparent carapace allowing examination of the male reproductive system of Trigonoplax unguiformis ( Fig. 58E ) unambiguously shows a true sternal emergence of the male duct, analogous to the thoracotreme disposition. Hymenosomatoids are thus problematic because a thoracotreme status cannot be retained and it is evident that there is a close relationship with crabs such as majoids (e.g., inachoidids and inachids) and dorippoids, which indicates a eubrachyuran, heterotreme affiliation. It is therefore assumed that a sternal male gonopore has evolved homoplasically in the Hymenosomatoidea and in the Thoracotremata ( Guinot 2011b). As the Hymenosomatidae is for now the only known family in Hymenosomatoidea , the two nomina are interchangeably used in the present text. See Modalities of penis protection: “Sternitreme” protection; Monophyletic Heterotremata: Superfamily Hymenosomatoidea ; Position of the Hymenosomatoidea within the Brachyura ; Affinities between Dorippoidea and Hymenosomatoidea ; Affinities between Hymenosomatoidea and Inachoididae ; Carcinisation and its outcomes: Cephalic condensation).

Figures

FIGURE 29. Male gonopore (A, B) and dorsal platelets of the abdomen (C–E) in Hymenosomatidae. A, Cancrocaeca xenomorpha Ng, 1991, male 3.9 × 4.6 mm, paratype, Indonesia, Sulawesi (MNHN-B24450); B, Odiomaris pilosus (A. Milne- Edwards, 1873) (Odiomarinae), male 20.0 × 22.6 mm, New Caledonia (MNHN-B26146); C–E, same data as B: abdomen in dorsal and ventral views; notice on pleotelson (somite 6 fused to telson) the vestigial uropod as intercalated, dorsal platelet, with socket situated beneath, and uropod (D) with electron microscope (all after Guinot & Richer de Forges 1997: figs. 5B–D, 9A, B). a.c., sterno-abdominal cavity; cx5, P5 coxa; g, gonopore; G1, first gonopod; p, uropod as dorsal platelet; pt, pleotelson; s, socket; 6–8, thoracic sternites 6–8; 6/7, 7/8, thoracic sternal sutures 6/7, 7/8. Scale bar: 100µm (E).

FIGURE 48. Location of vulvae. A–C, anterior displacement: A, Anasimus latus Rathbun, 1894 (Inachoididae), female 18.4 × 14.0 mm, French Guiana (MNHN-B17807); B, Capartiella longipes (Capart, 1951) (Inachidae), ovig. female 9.4 × 8.1 mm, Nigeria (MNHN-B19602). C, Halicarcinus planatus (Fabricius, 1775) (Hymenosomatidae), female 14.0 × 19 mm, South Pacific, Campbell I. (MNHN-B25960) (schematic); D, Hiroia krempfi Fize & Serène, 1956 (Cryptochiridae), female, Palau: vulvae not widely separated and sternal suture 7/8 complete (schematic, modified from Kropp 1990: fig. 6c); E, Pseudohapalocarcinus ransoni (Fize & Serène, 1956) (Cryptochiridae), female, Guam: vulvae located apart on broad thoracic sternite 6 (schematic, modified from Kropp 1990: fig. 12c). j, sternum/pterygostome junction; m.l., median line; v, vulva; 3–8, thoracic sternites 3–8; 4/5–7/8, interrupted thoracic sternal sutures 4/5–7/8; w, sternal wall.

FIGURE 58. Male reproductive system in Hymenosomatoidea (A, B, E), Pinnotheroidea (C, D), and male gonopores in Cryptochiroidea (F). A, B, dissection of Odiomaris pilosus (A. Milne-Edwards, 1873), male 11.0 × 14.0 mm, New Caledonia, Wé Waalu River (MNHN-B32604): ejaculatory duct and penis (highlighted in B); C, D, dissection of Dissodactylus crinitichelis Moreira, 1901, male 4.6 × 7.0 mm, Brazil (MZUSP 24231): ejaculatory duct (highlighted in D). E, testis and vas deferens as seen through the transparent carapace of Trigonoplax unguiformis (De Haan, 1839), male 6.1 × 7.3 mm, Western Australia (USNM 184973); F, Utinomiella dimorpha (Henderson, 1906): male gonopores perforating sternite 8 far from suture 7/8 (modified from Henderson 1906: pl. 8, fig. 8, as Cryptochirus dimorphus). cx1, cx5, P1, P5 coxae; e.d., ejaculatory duct; g, gonopore; p, penis; t, testis; 4–8, thoracic sternites 4–8; 4/5–7/8, interrupted thoracic sternal sutures 4/5–7/8. Scale bars: 1 mm (A, B); 4 mm (C, D).