Setozius Ng & Ahyong, 2013, gen. nov.

Setozius gen. nov.

Type species. Setozius incertus gen. et sp. nov., by monotypy.

Diagnosis. Carapace subcircular, wider than long, dorsal surface with regions poorly indicated, covered with numerous long and short stiff setae (Fig. 1 A); front bilobed, each lobe with 4 distinct sharp granules (Fig. 1 A); orbits relatively large (Figs. 1 A, B; 3B); anterolateral margin (including external orbital tooth) with 5 sharp granules (Fig. 1 A); posterior margin of epistome with 4 broad lobes (Figs. 1 B, 3B); endostome with distinct oblique ridges (Fig. 1 B). Third maxilliped covered with short and long stiff setae, inner margin of merus with prominent sharp tooth and small granules, anteroexternal angle auriculiform, exopod stout with long flagellum (Fig. 3 A). Outer surfaces of left cheliped manus, carpus and merus covered with numerous long and short stiff setae; manus covered with large, sharp conical granules (Figs. 1 A, 2A). Ambulatory legs relatively short, covered with short and long stiff setae, all segments unarmed (Fig. 2 C). Anterior thoracic sternum (sternites 1–4) length subequal to width (as measured at base of episternites 4 at point of articulation with coxal condyle); apex forming obtuse angle; sternites 1 and 2 fused, suture present between sternites 2 and 3; sternites 3 and 4 with sutures visible only laterally, sternite 4 with shallow longitudinal depression anterior to sternoabdominal cavity (Fig. 3 C); sternoabdominal cavity reaching anteriorly to level of anterior margins of coxae of first ambulatory legs (Fig. 1 C). Abdomen transversely narrow, all somites and telson free (Fig. 3 D). G1 gently sinuous, slender, lateral margins lined with short spines (Fig. 3 E, F); G2 about 0.4 times length of G1 (Fig. 3 G, H).

Etymology. The name is derived from an arbritary combination of the Latin for “setae” and the generic name Ozius. Gender masculine.

Remarks. The overall habitus of Setozius closely resembles Pilumnus, especially in the general carapace features and the strongly setose body. Many genera of brachyurans previously classified in Pilumnus Leach, 1815, and Pilumnidae are now referred to other families, e.g., Eupilumnus Kossmann, 1877 (= Globopilumnus Balss, 1933) (in Oziidae Dana, 1851), Parapilumnus De Man, 1895 (now in Acidopsidae), Pilumnoides Lucas, in H. Milne Edwards & Lucas, 1844 (now in Pilumnoididae Guinot & Macpherson, 1987), Rhithropanopeus Rathbun, 1898 (now in Panopeidae Ortmann, 1893), Forestiana Guinot & Low, 2010 (= Forestia Guinot, 1976), Heteractaea Lockington, 1877, Lipkemedaeus Števċiċ, 2011, Garthiope Guinot, 1990, Microcassiope Guinot, 1967, Polydectus H. Milne Edwards, 1837, and Cymo De Haan, 1833 (now in Xanthidae MacLeay, 1838) (see Ng et al. 2008). That general carapace habitus is not a good indicator of phylogenetic affinities among xanthids has already been well demonstrated by Lai et al. (2011) in their study of numerous xanthid genera.

Three characters indicate that Setozius gen. nov. belongs in the superfamily Pseudozioidea Alcock, 1898, as defined at present (Ng et al. 2008): a male abdomen with all the somites and telson free and not fused (Fig. 3 D), a slender G1 that is armed with only small spinules (Fig. 3 E, F), and a relatively long G2 with a long basal segment and no distal segment (Fig. 3 G, H). The Pseudozioidea currently contains three families: Pseudoziidae Alcock, 1898, Pilumnoididae Guinot & Macpherson, 1987, and Planopilumnidae Serène, 1984. The systematic position of the superfamily and three families has been discussed at length by Ng et al. (2008: 179), Ng (2010: 33–34) and Ng & Kazmi (2010: 586).

The three genera in Pseudoziidae, Euryozius Miers, 1886, Flindersoplax Davie, 1989, and Pseudozius Dana, 1851, differ markedly in appearance from Setozius gen. nov.: their carapaces are distinctly ovate with low lateral lobes and teeth (versus subcircular with anterolateral spines in Setozius gen. nov., Fig. 1 A), they do not have long stiff setae covering the carapace and pereiopods (versus with dense stiff setae in Setozius gen. nov., Figs. 1, 2), the outer surfaces of the chelipeds are smooth or rugose (versus with numerous sharp tubercles in Setozius gen. nov., Figs. 1 A, 2A), the apex of the male thoracic sternum tapers to a narrow acute point (obtuse angle in Setozius gen. nov., Figs. 1 C, 3C), the length of thoracic sternites 1–4 is distinctly less than the width as measured at base of episternites 4 at point of articulation with coxal condyle (versus subequal in Setozius gen. nov.), and the male abdomen is relatively broader than in the new genus (cf. Serène 1984: pls. 48A, B; Ng & Wang 1994: figs. 1a, b, 2, 3, 4a, 5–7; Davie 1989: figs. 11a, d, e–g, 12; Davie 1993: text-fig. 12, pl. 13; Ng & Liao 2002: figs. 1, 2, 3a–c). The Planopilumnidae currently contains Planopilumnus Balss, 1933, Rathbunaria Ward, 1933, Platychelonion Crosnier & Guinot, 1969, and Haemocinus Ng, 2003. Setozius gen. nov., however, differs markedly from these genera in having a more rounded carapace (versus distinctly quadrate in planopilumnids), the presence of numerous long stiff setae on the carapace and pereiopods (versus with dense short stiff or soft setae in planopilumnids), the outer surfaces of the chelipeds are covered with numerous sharp tubercles (versus smooth, rugose or granular in planopilumnids), proportionately short ambulatory legs (versus relatively long in planopilumnids), the male anterior thoracic sternum is proportionally narrow, with subequal length and width l (versus distinctly broader than long in planopilumnids), the male abdomen is proportionally narrower, and the distal part of the G1 is not flared as in planopilumnids (cf. Ng 2003: figs. 1–7; Ng 2010: figs. 1–8, 10–12; Ng & Kazmi 2010: figs. 1–6).

Pilumnoides Lucas, in H. Milne Edwards & Lucas, 1844 (the only genus in Pilumnoididae), most closely resembles Setozius gen. nov., especially in the more rounded and setose carapace, similar length:width proportions of thoracic sternites 1–4, and a narrow male abdomen. All species of Pilumnoides, however, have an anterolateral carapace margin lined with teeth and not spines, the setae are not stiff, less dense and concentrated on the lateral parts rather than over the entire surface, the orbits and eyes are proportionately smaller, the apex of the thoracic sternum tapers to an acute point (versus obtusely angled) and the inner margin of the merus of the third maxilliped is not granulated (cf. Garth 1940: pl. 23; Guinot & Macpherson 1987: text-fig. 4, pls. 1, 2). These differences do not appear to be significant at the family level, and therefore it seems best to place Setozius gen. nov. in Pilumnoididae for the time being. The Pilumnoididae was previously represented only by its type genus, with all the known species occuring in the Atlantic and eastern Pacific (Guinot & Macpherson 1987). No pilumnoidid was hitherto known from the Indo-West Pacific, so the placement of Setozius gen. nov. in this family is noteworthy.

The discovery of the new genus of crab from an artificial substrate, let alone it being the first of its family from the Indo-West Pacific, highlights the significant amount of taxonomic research that will still need to done in the region. Although the precise provenance of Setozius gen. nov. is unknown, the source craft operated in the Timor Sea and South China Sea prior to reaching Singapore so it is likely to come have come from either. The decapod and stomatopod fauna associated with Setozius gen. nov. is all Indo-West Pacific (mostly Australasian) in origin, with a composition more consistent with that of the Timor Sea than South China Sea (Yeo et al. 2009).

With regard to the rounded carapace shape, short ambulatory legs and the presence of numerous long stiff setae, Setozius gen. nov. superficially resembles some species of the oziid Eupilumnus (Eriphioidea), notably E. actumnoides (A. Milne-Edwards, 1873) and E. globosus (Dana, 1852) (see Guinot-Dumortier 1960). Setozius gen. nov., however, is immediately distinguished by having a sharp spine at the junction of the antero- and posterolateral margins, a relatively more slender G1 and a G2 that does not have a long distal segment (cf. Guinot- Dumortier 1960: figs. 1–8, 12, 13).

Comparative material. Specimens of pseudoziids and planopilumnids listed in Ng & Wang (1994), Ng & Liao (2002), Ng (2003), Ng (2010), Ng & Kazmi (2010). Globopilumnus globosus: 1 male (10.2 × 8.6 mm), 1 female (9.2 × 7.6 mm) (ZRC), Guam, coll. G. Paulay, 1986.— Pilumnoides perlatus (Poeppig, 1836): 1 female (ZRC 2001.768), Iquique, Chile, coll. G. Guimert, June 2001.— Pilumnoides hassleri A. Milne-Edwards, 1880: 1 male, 1 ovigerous female (ZRC 2001.1001), south Atlantic Ocean off Argentina, station 16g, 37°00’S 55°21’W, 69 m, coll Calypso, 29 December 1961.— Pilumnoides rubus Guinot & Macpherson, 1987: 4 females (1 ovigerous) (ZRC 2012.0691), northern Namibia, Rocky Point, coll. E. Macpherson, 24 February 1986.