Sphenomerides Rathbun 1897
Creators: name: Ng, Peter K. L.
name: Ahyong, Shane T.
name: Castro, Peter
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Trapeziidae
Sphenomerides

description: Sphenomerides Rathbun, 1897   
 Sphenomerus Wood-Mason in Wood-Mason & Alcock, 1891: 263 (name pre-occupied by Sphenomerus Candèze, 1859 [Coleoptera]); Alcock, 1898: 227.   
 Sphenomerides Rathbun, 1897: 164 (replacement name for Sphenomerus Wood-Mason in Wood-Mason & Alcock, 1891); Alcock, 1899: 65; Serène, 1973: 207, 1984: 289; Castro et al., 2004: 59; Ng et al., 2008: 185; Poore & Ahyong, 2023: 730, fig. 14.139g.   
 Type species. Sphenomerus trapezioides Wood-Mason in Wood-Mason & Alcock, 1891, by monotypy; gender masculine).   
 Diagnosis. As for subfamily.   
 Remarks. As discussed earlier for Ectaesthesiidae, Sphenomerides is not included in Calocarcinidae mainly because its P2–5 dactylus possesses transverse comb-like rows of feeding setae, albeit restricted to the flexor margin only (Fig. 12E, F), features absent in Calocarcinus and Philippicarcinus. In addition, the posterior margin of the epistome is proportionally wider in Calocarcinus and Philippicarcinus than in Sphenomerides (Figs. 5D vs Fig. 5C), the maxilliped 3 merus is quadrate and wider than long, with the ischium rectangular (Fig. 6E) (merus longer than wide with the ischium trapezoidal in Sphenomerides; Fig. 6D), the flexor margin of the cheliped merus is smooth and unarmed (spinate in Sphenomerides; Fig. 12A), there is always a distinct suture separating thoracic sternites 2 and 3 (Fig. 7F, G) (no suture visible in Sphenomerides; Fig. 7E), male pleonal somite 2 is proportionally much broader than in Sphenomerides; Fig. D, E); the sutures across male pleonal somites 3–5 are visible although they are immobile (Fig. 8E) (sutures conspicuously shallow to hardly visible in Sphenomerides; Figs. 8D, 12D), and the G2 is three-quarters to subequal to the length of the G1 with the basal portion elongated (Fig. 9L, N) (short, being only about one-quarter the length of the G 1 in Sphenomerides; Fig. 9J). Only one of the above features of Sphenomerides is different from typical trapeziids: the absence of suture between thoracic sternites 2 and 3 (Fig. 7E). This character, however, can also be observed in some species of Trapezia and Quadrella so it is not unique in the family. Sphenomerides is also unusual among trapeziids in its comparatively high carapace, with the dorsal surface prominently convex (Fig. 12B). All other confamilials are distinctly flatter. In most other aspects, including the relatively slender G1 and comparatively narrow maxilliped 3 merus, Sphenomerides is close to the quadrellines. However, the inflated carapace and unusual distribution of the P2–5 feeding setae, being present on the flexor margin but absent from the facial surfaces (present in other trapeziids) are considered sufficient to justify placing Sphenomerides in its own subfamily within Trapeziidae.   
 No genetic data are yet available for Sphenomerides trapezioides.
description: Published as part of Ng, Peter K. L., Ahyong, Shane T. & Castro, Peter, 2023, Re-appraisal of the families and subfamilies of Trapezioidea Miers, 1886, with establishment of a new family, Ectaesthesiidae (Crustacea: Decapoda: Brachyura), pp. 606-631 in Raffles Bulletin of Zoology 71 on page 622, DOI: 10.26107/RBZ-2023-0047, http://zenodo.org/record/10271307