Opusia indica Alcock 1900

Opusia indica (Alcock, 1900)

(Figs. 1 A, 2)

Tylodiplax indica Alcock, 1900: 374. – Alcock & Anderson 1895: pl. 64 fig. 2. – Tesch 1918: 69. – Stephensen 1946: 192, fig. 58B–G. – Serène 1968: 101 (in list).

? Serenella indica — Manning & Holthuis 1981: 212.

" Tylodiplax " indica — Ng et al. 2008: 234.

Material examined. PAKISTAN: 1 male (6.9 x 10.1 mm), 1 female (6.8 x 10.1 mm) (USNM 191107), Pasni Creek, Karachi, coll. Khalid & Shamim, 13 December 1981; 1 male (5.9 x 8.8 mm), 2 females (4.5 x 6.7 mm, 5.1 x 7.1 mm) (USNM 205945), mangrove of Korangi Creek, 19 January 1982. IRAQ: 4 males (3.8 – 6.6 mm x 5.6 – 11.3 mm), 2 females (5.1 x 8.2 mm, 7.3 x 12.0 mm) (ZRC 2009.832), Ras Al-Pisha, 29°55'40.01"N 48°36'37.29"E, Fao Region (Shatt Al-Arab), Iraq, coll. M. D. Naser, 2009. IRAN: 1 male (4.5 x 6.7 mm), 1 female (4.7 x 6.9 mm), 2 juveniles (3.0 x 4.5mm, 3.4 x 4.5mm) (RMNH D 39210), Persian Gulf, don. M. T. Abbaspour, September 1989.

Type locality. Karachi, Pakistan.

Description. Carapace broader (about 1.5 times) than long, dorsal surface (particularly median region) with small pits, folds, with long plumose setae, setae denser on frontal, hepatic, branchial regions; epigastric lobes indistinct, not distinctly swollen; 2 short, transverse parallel grooves on either side of gastric region, forming "crimped" structure; short, deeper, oblique groove on either side of posterior margin of cardiac region. Anterolateral margin defined by row of granules ending about halfway to posterior, larger granules on median part of anterolateral margin, forming small angle; pterygostomial region swollen beyond anterolateral margin, more convex on median portion, forming small protuberance, visible dorsally; posterolateral margin strongly convex, rounded; posterior margin gently sinuous, thickened, with thin submarginal ridge of coalesced granules. Front straight, with thickened margin, bearing long, plumose setae, orbital region at base of front convex, junction of base of front, supraorbital margin broadly rounded, not distinct; frontomedial projection triangular, ending in truncate tip.

Cornea small, eyestalks relatively long, slender, with long plumose setae. Orbit about as wide as front, external orbital tooth distinct, triangular; supraorbital margin sinuous, beaded; infraorbital margin setose, with widely spaced granules, inner two-thirds cristate, inner infraorbital tooth triangular, distinctly demarcated from rest of infraorbital margin by broadly triangular notch; suborbital ridge defined by large, rounded granules, not visible dorsally.

Pterygostomian region with short setae, finely granular, anterior region with transverse, open sulcus, anterior margin clearly separated from lateral margins of epistome. Epistome with narrow anterior half, latter slightly sunken, separated from posterior half by transverse ridge, anterior margin (forming lower margin of antennular fossa) granular, posteromedial tooth large, acute, moderately narrow, posterior margin on either side of tooth lobate, lobes located under basal segment of antenna.

Third maxilliped inner margins thick, ischium broadening gradually from proximal to distal, inner distal angle slightly produced, inner margin setose, with row of short setae close to outer half of distal margin; merus about half ischium length along inner margin, outer distal angle well developed, expanded to form rounded lobe.

Chelipeds slender, outer margins with long plumose setae, chela palm smooth, with ridge, row of short, thick setae on outer lower surface extending to immovable finger; fingers slender, about twice palm length, cutting edges blade-like, tips sharp, weakly spatulate, with submarginal row of setae close to cutting edges, movable finger outer surface with short row of short, thick setae close proximal half. Female chelipeds relatively more slender, less setose than in male.

Ambulatory legs thick, slightly flattened laterally; P3 most setose; P5 shortest; P2, P3 ischia with large tooth on posterior margin of ventral surface, P3 ischium with larger tooth, granular margin; meri with granular dorsal posterior margin, P3 merus most granular. Female legs relatively less setose than in male.

Surface of male thoracic sternum sparsely granular; sternites 1–3 fused, compressed, anterior edge evenly rounded, distinct groove separating fused sternites 1, 2 from transversely very narrow sternite 3; anterolateral margin of sternite 3 with shallow subovate depression. Male abdomen with all sutures clear, complete, somite 1 slightly wider than somite 2, somite 2 separated from somite 3 by notch on either side of lateral margin, somites 3–5 immovable, although sutures between them distinct, complete, somite 4 trapezoidal with small lobe on either side, somite 5 with constriction close to proximal end, somite 6 with sides weakly convex, telson about as long as broad. Female abdomen rounded, with all somites free; telson broadly triangular, with rounded apex.

G1 with conical apex, tip with row of small, thick spines, strong, backward curving spines distal to apex, large mushroom-shaped spines subapically on inner side, decreasing in size proximally.

Remarks. Alcock (1900) did not designate a holotype from the two male specimens he examined. His specimens, which are not located in NHM, are probably still in the Zoological Survey of India (Calcutta). Nevertheless, the specimens examined in this study match his description and figures very well and we have no doubt they are conspecific.

In describing T. indica, Alcock (1900: 374) stated that he was unable to provide a complete diagnosis of the two male specimens because “their chelipeds are still of the female Macrophthalmus type ". The results of this study show, however, that sexual dimorphism of the chelipeds is not distinct in this species. All male specimens examined, including the largest (6.9 x 10.1 mm; USNM 191107) which was fully mature, had only slightly less slender chelipeds than in the females (Fig. 2 F). This is in accordance with Stephensen's (1946: 193) observation that "The chela are equal, very slender and small, even in the adult male, rather smaller than larger than in the "Investigator" figure. There is no sexual difference in the chelipeds".

Stephensen (1946: 193) also mentioned that in his Iranian specimens, "all sutures are distinct, and no doubt all the 7 segments are free" in the male abdomen. However, the abdomens of the male specimens examined appear to be more in agreement with Alcock's (1900: 374) diagnosis, which states that the third to fifth somites are fused, "but without obliteration of sutures" (Fig. 2 C). Movement between these "fused" somites is very much limited relative to the other freely mobile somites and are, for all effects and purposes, fused.

Habitat and biology. According to the list of material given by Stephensen (1946: 193), the specimens were collected from intertidal estuarine habitats with clay and sandy soft bottoms. The collection site at Ras Al-Pisha is an intertidal area near the open coast, with salinity averaging 32‰, and the substrate is soft silty clay (see also habitat notes for Nasima dotilliformis).

Geographical distribution. Iran (Iranian Gulf, Strait of Hormuz, Gulf of Oman) and Karachi, Pakistan.