Selwynia Borradaile 1903
Creators: name: Ng, Peter K. L.
name: Rahayu, Dwi Listyo
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pilumnidae
Selwynia

description: Selwynia Borradaile, 1903
Selwynia Borradaile, 1903: 430 [type species: Selwynia laevis Borradaile, 1903, by monotypy]; Ng 1997: 98; Ng et al. 2008: 144 (list); Ng & Clark 2014: 1.
Aphanodactylus Tesch, 1918: 283 [type species: Aphanodactylus sibogae Tesch, 1918, by monotypy]; Schmitt et al. 1973: 127 (in list); Ng et al. 2008: 247; Ng & Naruse 2009: 284; Ahyong & Ng 2009: 34; Castro, 2015: 553 (in list).
Diagnosis. Carapace wide, ovate, males 1.4–1.5 times wider than long, females 1.6–1.9 times wider than long; lateral margins cristate or subcristate, but not continuous to external orbital end; surface smooth, glabrous, with few scattered pits. Front narrow, deflexed broadly triangular in frontal view; straight to weakly sinuous in dorsal view. Orbit transverse; margins entire, unarmed; infraorbital margin mesially terminating in acute angle; supraorbital margin demarcated from antennular fossa by even curve; infraorbital and supraorbital margins not extending laterally beyond cornea or continuing laterally or posteriorly beyond orbit. Eyes short, mobile, fully. Antennules articulating transversely to slightly obliquely. Epistome short, medially sunken. Third maxilliped ischium longer than merus, both subquadrate. Thoracic sternites 1, 2 completely fused, broadly angular anteriorly; sternites 2/3 demarcated by shallow groove; sternites 3/4 fused, laterally unarmed; sternites 4–8 demarcated by narrow grooves, those demarcating sternites 4–7 incomplete medially; without longitudinal groove. Cheliped merus and carpus unarmed, with sparse plumose setae. P2–5 similar in shape, P3 longest; meri about twice as long as high, as long as or slightly longer than respective carpi and propodi combined; with plumose setae on flexor and extensor margins; meri with or without teeth along flexor margin; P5 markedly shorter than preceding legs; P2–5 with short spines on distoflexor angle of propodus opposing dactylus; dactylus very short, claw-like. Male abdomen simple, triangular; telson and all somites free; widest at somite 1; thoracic sternite 8 exposed when abdomen closed. Female abdomen with telson, all somites freely articulating, widest at somite 4. Vulva ovate, maximum width, may exceed half width of sternite 6. G1 simple, slender, broadly curved. G2 small, about 1/3 length of G1, slender, apex blunt. (Modified from Ahyong & Ng 2009: 36).
Remarks. Selwynia is the most species-rich genus, with six described species, with another two described here. As discussed by Ng & Naruse (2009), the various species of Selwynia (as Aphanodactylus) closely resemble each other in general appearance. The shape of the G1 is also quite similar in most species. Ng et al. (2010) argued that most of characters used by Konishi & Noda (1999) to separate the species of Selwynia (as Aphanodactylus) such as width to length ratio of the carapace, depth and extent of dorsal punctae on the carapace, shape of the frontal margin, and the number of antennular segments were unreliable, although the ventral armature of the merus of P2–P5 was useful at least to separate S. edmondsoni and S. lomiae (Konishi & Noda, 1999), but not S. sibogae (Tesch, 1918). Instead, the species of Selwynia can be distinguished by the shape of the carapace, ambulatory leg proportions and armature, structure of the third maxilliped, and subtle differences in the shape of the G1. Unfortunately, no single species is represented by a large sample size of various size-groups, so variation within a species is not well understood. For now, the differences observed between taxa are regarded as significant at the species level.
For females, most species have teeth on the flexor margins of P2–P4, with denticles of varying numbers. In species like S. sibogae, S. loimiae, S. panglao, and S. edmondsoni, there are two distinct teeth on each merus with varying numbers of denticles (e.g., Figs. 4 G, H, J, K, 5C; Konishi & Noda 1999: fig. 1e; Ng et al. 2010: fig. 1D; Ng & Naruse 2009: fig. 1a). In S. madang n. sp., and S. punctata n. sp., there is one distinct tooth, and several or no denticles on each merus (e.g., Figs. 12 G, 16H; Ng & Naruse 2009: table 1; Ahyong & Ng 2009: fig. 2E). As for the P5, females generally have an unarmed flexor margin, although the right merus of one specimen of a female S. madang n. sp. (the holotype) has a small denticle (Fig. 12 H). There also seems to be variation in S. loimiae, with the margin unarmed or with one prominent tooth and denticles (cf. Ng et al. 2010). Selwynia edmondsoni is distinctive among its congeners in that the flexor margin of the P5 merus has a large proximal tooth with several denticles (Fig. 7 E). For males, the P2–P4 flexor margin of the merus has 2–4 teeth and several or no denticles in S. sibogae and S. panglao, with one tooth and low denticles in S. punctata n. sp. and S. edmondsoni, only several denticles in S. madang n. sp., almost unarmed or with one denticle in S. laevis (Figs. 4 C, 7C, D, 12C, 16C; Ng & Naruse 2009: fig. 3d; Ng & Clark 2014: fig. 2B–G). The flexor margin of the P5 merus in most of the species is unarmed, with the exception of S. edmondsoni, S. madang n. sp., and S. punctata n. sp., which has only one distinct tooth and/or denticles; being largest in S. edmondsoni (Figs. 7 E, 9A, 16D). Selwynia madang n. sp. is unusual in that the basis-ischium of the female P5 also has a distinct small or large denticle on the ventral margin (Fig. 12 H). An unusual character present only in male S. edmondsoni is that the anterior margin of the flexor surface is armed with three teeth (Fig. 7 C); in all congeners, even in females of S. edmondsoni, this part is smooth (e.g., Figs. 4 H, 12C, 16H; Ng & Naruse 2009: fig. 3d; Ng & Clark 2014: fig. 2). The extensor margin of the merus of the P2–P5, it is usually unarmed, although the surface is granular and uneven. In S. sibogae and S. madang n. sp., the proximal part of this margin can be uneven but it is not dentate. The only species in which the extensor margin of P2 and P3 is distinctly dentiform is S. panglao (see Ng & Naruse 2009: 3d).
Comparative material. Selwynia laevis Borradaile, 1903: see Ng & Clark (2014); Selwynia loimiae (Konishi & Noda, 1999): see Ahyong & Ng (2009); Ng et al. (2010); Selwynia panglao (Ng & Naruse, 2009): see Ng & Naruse (2009).
description: Published as part of Ng, Peter K. L. & Rahayu, Dwi Listyo, 2016, On the genera Selwynia Borradaile, 1903, and Gandoa Kammerer, 2006, with descriptions of two new species from Papua New Guinea and French Polynesia (Crustacea: Decapoda: Brachyura: Aphanodactylidae), pp. 339-370 in Zootaxa 4092 (3) on pages 340-342, DOI: 10.11646/zootaxa.4092.3.2, http://zenodo.org/record/254902