Setozius incertus Ng & Ahyong, 2013, sp. nov.
Creators: name: Ng, Peter K. L.
name: Ahyong, Shane T.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pilumnoididae
Setozius
Setozius incertus

description: Setozius incertus sp. nov.
(Figs. 1–3)
Material examined. Holotype: male (16.3 × 13.2 mm) (ZRC), from fouling community on semisubmersible oil platform in Singapore shipyard, ostensibly from Timor Sea or South China Sea, coll. D. Lane, December 1977 (see Yeo et al. 2009: 180).
Description. Carapace subcircular, wider than long; dorsal surface with regions poorly defined, weakly convex, almost smooth, covered with numerous long and short stiff setae that do not completely obscure surface and margins; branchial regions covered with low rounded granules (Fig. 1 A). Front distinctly produced, extending beyond orbits; bilobed, each lobe with convex margin, lined with 4 distinct sharp granules; lobes separated by Vshaped cleft; margin lined with numerous stiff setae which almost obscures margin (Fig. 1 A). Supraorbital margin sinuous, forming 3 low, rounded lobes separated distinct shallow clefts, inner supraobital angle almost contiguous with frontal margin, marked only by low angle (Fig. 1 A). Infraorbital margin distinctly granular, with 2 prominent sharp granules (Figs. 1 B, 3B). Orbits relatively large, sloping posteriorly from dorsal view; eyes well-developed, peduncle with 2 small rounded granules on dorso-distal part; cornea globose (Figs. 1 A, B, 3B). Anterolateral margin (including external orbital tooth) with 5 sharp granules, last 2 largest, second smallest (Fig. 1 A). Posterolateral margin almost straight, strongly converging towards posterior carapace margin (Fig. 1 A). Posterior carapace margin gently convex, lined with small rounded granules (Fig. 1 A). Pterygostomial and sub-orbital regions with scattered small rounded granules, separated by distinct row of rounded granules (Figs. 1 B, 3B). Basal antennal article quadrate, outer surface with group of raised granules, mobile, not completely filling orbital hiatus; third article subrectangular; flagellum long, longer than length of orbit, flagellum inside orbit (Figs. 1 B, 3B). Antennules folding transversely; lower margin of basal antennular article lined with small granules; lower margin of antennular fossa lined with small rounded granules (Figs. 1 B, 3B). Posterior margin of epistome with 4 broad lobes, separated by distinct fissures; median 2 forming broad median triangular structure, depressed into endostome (Figs. 1 B, 3B). Endostome with distinct oblique ridges (Fig. 1 B).
Third maxilliped relatively short, covered with both short and long stiff setae; ischium separated from basis by distinct suture; basis with ventral margin denticulated; ischium with shallow submedian oblique sulcus, inner margin distinctly dentate, lined with stiff setae (Fig. 3 A). Merus subquadrate, median part slightly depressed, margins finely granular; inner margin with prominent sharp tooth and several granules; anteroexternal angle auriculiform (Fig. 3 A). Exopod stout, distal margins granular; tip reaching beyond edge of merus; flagellum long (Fig. 3 A).
Right cheliped missing; outer surfaces of left manus, carpus, merus covered with numerous long and short stiff setae which partially obscures surface, margins (Figs. 1 A, 2A, B). Basis-ischium fused, suture visible; surface smooth; inner margin of ischium lined with small granules. Merus surface granular, separated from basis-ischium by suture; short, upper margin granular, with strong subdistal tooth, separated by deep cleft (Fig. 2 B). Carpus short, inner distal angle with sharp tubercle, outer surface with large, sharp conical granules on ventral half; dorsal margin with row of sharp granules (Fig. 1 A). Chela short; surface of manus covered with large, sharp conical granules, those closer to fingers relatively smaller, slightly curved anteriorly, dorsal margin with granules elongated to form short spines, inner surface with scattered rounded granules; fingers shorter than palm, not pigmented, tips curved; cutting edges with large blade like teeth separated by deep fissures; dorsal margin of dactylus with short spines, gradually decreasing in size towards tip; subventral margin of pollex with row of sharp, similarly-sized granules (Fig. 2 A).
Ambulatory legs relatively short, second leg longest; outer surface smooth, covered with short and long stiff setae, not completely obscuring surface (Fig. 1 A). Merus unarmed; dorsal margin of first to third legs with low subdistal angle, not tooth or spine; dorsal margin of fourth leg entire (Fig. 2 C). Carpus unarmed, with longitudinal depression subparallel to margin (Fig. 2 C). Propodus short, ovate, unarmed (Fig. 2 C). No discernible dactylopropodal lock; dactylus short, proximal two-thirds covered with setae with distal corneous part glabrous, sharp, hook-like (Fig. 2 C).
Anterior thoracic sternum covered with short and long stiff setae, length of sternites 1–4 subequal to width as measured at base of episternites 4 at point of articulation with coxal condyle (Figs. 1 C, 3C). Sternites 1 and 2 completely fused, no suture discernible, apex an obtuse angle; surface covered with small rounded granules (Figs. 1 C, 3C). Deep sinuous suture present between sternites 2 and 3, surface of sternite 3 granular (Figs. 1 C, 3C). Sternites 3 and 4 with sutures visible only laterally; anterior and lateral surfaces of sternite 4 granular, sternite 4 with shallow longitudinal depression anterior to sternoabdominal cavity (Figs. 1 C, 3C). Sternites 4/5 medially interrupted by deep pit; sternites 5/6 medially interrupted, separated by narrow plate; sternites 6-8 entire; longitudinal groove separate sternites 7/8. Press-button of male abdominal locking mechanism distinct, peg-like, on posterior margin of sternite 5. Sternoabdominal cavity reaching to imaginary line connecting anterior margins of coxae of first ambulatory legs (Fig. 1 C). Penis relatively short, arising directly from base of coxa of fourth ambulatory leg, adjacent to condyle.
Abdomen transversely narrow, all somites and telson free (Fig. 3 D). Somite 1 medially narrow, laterally expanded; somite 2 subtrapezoidal, somites 1 and 2 completely spanning thoracic sternum, completely hiding thoracic sternite 8 when abdomen closed (Fig. 3 D). Somites 3 and 4 trapezoidal with gently sinuous lateral margins; somite 5 rectangular with gently concave lateral margins; somite 6 quadrate with concave lateral margins, distal margin wider than proximal margin (Fig. 3 D). Telson semicircular with gently convex lateral margins and rounded tip (Fig. 3 D).
G1 gently sinuous, slender, lateral margins lined with short spines, long setae absent; distal part subtruncate with open distal tip (Fig. 3 E, F). G2 about 0.4 times length of G1, distal part spatuliform, without distal segment (Fig. 3 G, H).
Female unknown.
Etymology. The specific epithet, incertus, Latin for “uncertain”, alludes to the uncertain provenance of the species.
Remarks. Little is known about the ecology of Setozius incertus gen. et sp. nov. It was collected amongst fouling organisms on a semisubmersible oil platform. The fauna are typical of coral reefs (Yeo et al. 2009). Setozius incertus gen. et sp. nov.is also likely associated with such habitats.
The close resemblance of Setozius incertus gen. et sp. nov. to members of the genus Pilumnus poses potential problems. The cosmopolitan genus Pilumnus is one of the largest in the Brachyura, with 140 recognised species and 23 synonyms; it is badly in need of a complete revision (see Ng et al. 2008; Ng 2010). Although these species have been checked during this study, the fact remains that some of these Pilumnus species are poorly known and it is possible that some may prove to be synonymous with the new species. These potentially synonymous species, however, will not change the status of the new genus.
description: Published as part of Ng, Peter K. L. & Ahyong, Shane T., 2013, Discovery of a new genus and new species of Indo-West Pacific pilumnoidid crab from a semisubmersible oil platform (Crustacea: Brachyura: Pseudozioidea), pp. 513-520 in Zootaxa 3682 (4) on pages 515-519, DOI: 10.11646/zootaxa.3682.4.2, http://zenodo.org/record/218155