Stenorhynchus, Lamarck, 1818

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 : 225-226

Status of Stenorhynchus and Stenorhynchinae Dana, 1851

The genus Stenorhynchus Lamarck, 1818 (type species: Cancer seticornis Herbst, 1788 , by subsequent designation, see Rathbun 1897; Garth & Holthuis 1963; Anonymous 1966), traditionally assigned to the Inachidae (e.g., Rathbun 1925; Monod 1956; Garth 1958; Yang 1976; Powers 1977; Manning & Holthuis 1981; Williams 1984; Felder 1973; Poupin 1994a; Cruz & Campos 2003; Ng, Guinot & Davie 2008; Felder et al. 2009; Hultgren et al. 2009; Wicksten 2011), must be referred to Inachoididae , with which it shares the above-mentioned traits ( Guinot 2012). The generic nomen Pactolus Leach, 1815 (type species by monotypy: Pactolus boscii Leach, 1815 ), based on a composite specimen including a carapace of Cancer seticornis Herbst, 1788 (see Leach 1815b: 19, 20, pl. 68), as well as the nomen Pactoliens, established with reservation by H. Milne Edwards (1837a: 167, 188) for a particular tribe of Anomura Aptérures , are not available ( Guinot 2012).

Although small and not salient, pleurites 5–8 are exposed beyond each side of the carapace and distinctly visible. They are smooth like the carapace, which rests on a gutter, and in males the second as well as the first abdominal somite are integrated into the cephalothorax, whereas several other somites are in the prolongation of the carapace, at least somites 1–4 and a portion of 5 in ovigerous females. The thoracic sternum/pterygostome junction is complete, and sternal extensions between P1 and P2, P2 and P3, P3 and P4, P4 and P5 connect the sternum to the laterally exposed pleurites. The carapace is practically naked, with fine, coloured lines, and there is no decoration behaviour, which is evidence that Stenorhynchus is much closer to the other inachoidids than to the inachids, which are active decorators (see Decoration behaviour). Stenorhynchus possesses the main characters that differentiate Inachoididae from Inachidae but also some distinctive features. The carapaces of the four known species of Stenorhynchus are less narrow and not sculpted as in other inachoidids and they prolong into an unpaired, long rostrum, only one small postocular spine is preent along the long “neck” (instead of a triangular postocular process), and the thoracic sternal suture 3/4 is very weak (instead of the marked suture prolonging into a deep depression or forming a boutonniere in other inachoidids) (see Affinities between Inachoididae and Inachidae , below). The expansion of the pleurites seems already present in the first crab stage of S. seticornis ( Yang 1976: fig. 7A).

The distribution of Stenorhynchus includes West Africa, the western Atlantic (from North Carolina to Argentina) and the eastern Pacific, whereas the other Inachoididae are exclusively known from the Atlantic and Pacific coasts of the Americas (except e.g., Pyromaia , some species of which are invasive, see Brockerhoff & McLay 2011). It is noteworthy that Inachoididae replace Dorippidae in the Americas, where it is completely absent and where Ethusidae , in contrast, is largely represented.

The status of Stenorhynchus (long assumed to be an Inachidae ) remained uncertain in the molecular study by Hultgren et al. (2009: 448, figs. 1, 2). The zoeae of Stenorhynchus spp. , unlike those of inachid genera, have no lateral carapace spines and exhibit antennae, maxillules, and telson fork that are distinctive; in addition, the megalopa develops functional uropods ( Yang 1976; Rice 1980, 1983, 1988; Paula & Cartaxana 1991). Larval characters of Stenorhynchus suggest its placement between the two larval groups recognised in Inachidae ( Rice 1980: 308) . Webber & Wear (1981: 370, 380) stated that the larvae of two Inachoididae , Anasimus and Pyromaia Stimpson, 1871 , “fall quite neatly between the Stenorhynchus species and Inachus , Achaeus and Macropodia ”, thus supported the view that Stenorhynchus fills such a gap (see Guinot & Richer de Forges 1997). The results were similar to those of Yang (1976: 167), in which zoeae of Stenorhynchus seticornis appeared to have more plesiomorphic characters than those of inachine genera such as Inachus , Achaeus Leach, 1817 , and Macropodia Leach, 1814 . Marques & Pohle (2003: 76, 78, figs. 1, 2), based on larval studies, discussed the conflicting position of Stenorhynchus among the Inachidae and supported the genus as basal to a clade of inachoidids. These results are congruent with the morphology of the adults, which provides evidence for the inclusion of Stenorhynchus in Inachoididae as well as the absence of decoration behaviour (see Decoration behaviour). Its placement in a separate inachoidid subfamily, Stenorhynchinae Dana, 1851 ( Dana 1851a: 432; see also 1852: 83), was discussed by Guinot (2012). Inachoidids with a triangular body and a grooved, ornamented carapace dorsal surface are included in Inachoidinae Dana, 1851 (type genus: Inachoides H. Milne Edwards & Lucas, 1842 ).

The long, unpaired rostrum of Stenorhynchus is an obvious resemblance with two fossil podotreme crabs from the Albian-Cenomanian, † Heeia Wright & Collins, 1972 , and † Viaia Artal, Van Bakel, Fraaije, Jagt & Klompmaker, 2012 , both of which were assigned to a new family, † Viaiidae Artal, Van Bakel, Fraaije, Jagt & Klompmaker, 2012 , tentatively included in †Glaessneropsoidea (see Schweitzer & Feldmann 2009b; see also Artal et al. 2012: 399, 402–404).