Scabrilucina victorialis (Melvill, 1899)

Taylor, John D. & Glover, Emily A., 2013, New lucinid bivalves from shallow and deeper water of the Indian and West Pacific Oceans (Mollusca, Bivalvia, Lucinidae), ZooKeys 326, pp. 69-90 : 71-73

Scabrilucina victorialis (Melvill, 1899) Figs 1-2, 3A

Cryptodon victorialis Melvill, 1899: 98-9, pl. 2, figs 9, 9a.

Loripes victorialis - Smith 1906: 256.

Loripes victorialis - Melvill and Standen 1907: 815.

Lucina victorialis - Oliver 1995: 235, fig. 1024.

Type material.

Holotype, left valve (NHMUK 1899.12.18.28), H 25.3 mm, L 23.5 mm.

Type locality.

Melvill (1899) p. 99 states 'near Karachi, and also Malcolm Inlet nr Muscat, Oman 24 fathoms’ (44 m) (Malcolm Inlet is Ghubbat al Ghazira).

Other material examined.

Northern Arabian Sea: 141 valves (MCZ 362493), 47 miles E of Duhat Sharjah, Oman, Arabian Sea, 50.5-52 fthms (92-95 m), Anton Brunn Cruise, 4b stn 255A (25°50'N, 57°07'E, 30 November 1963). 2 valves (USNM 716871), localityas above, Anton Brunn station 255A. 1 valve (NHMUK 99.2.18.10)25 fthms (45.7 m), 26°23'N, 54°53'E, Melvill collection. 1 valve (NHMUK) off Gwadhur (Gwadar), Pakistan, 70 fthms (128 m), Townsend collection. 4 valves, NHMUK, Gulf of Oman, Townsend collection. 1 valve (NHMUK 1906.10.12.90) Arabian Gulf, 47 fthms, Investigator station 346, ( Smith 1906).

Description.

Shell white, thin, often semi-translucent, H to 43 mm, L to 39 mm, higher than long, H/L = 1.03 ± SD 0.03 (n=17), moderately inflated T/L 0.27 ± SD 0.014 (n=17), outline subtrigonal in larger shells, juvenile shells subcircular. Posterior sulcus, prominent, deeply incised, with marginal sinus; anterior sulcus narrow and shallow. Sculpture of fine, closely spaced (200-500 µm apart), thin, sharp-edged, striated, commarginal lamellae (Figs 2 A–C) that narrow to around 30 µm at the distal edges and are slightly elevated along the posterior and anterior dorsal margins. Fine sediment is frequently trapped between lamellae. Protoconch (Fig. 2D): PI 150 mm, PI + PII 165 µm, PII with 2-3 growth increments. Lunule long, lanceolate and asymmetric, slightly larger in left valve. Ligament short, set in narrow groove. Hinge plate narrow, LV with 2 cardinal teeth, the anteriormost reduced and often obscured by ventral extension of lunule (Fig. 1 M–P), lateral teeth absent; RV with 1-2 small cardinal teeth, sometimes obscure, small anterior lateral tooth sometimes visible in younger shells (Fig. 1P). Anterior adductor muscle scar long, thin, tapering at ventral tip, detached for ½– ⅔ length and diverging ventrally at angle of 25-30° from pallial line, posterior adductor scar ovate. Pallial line broad, continuous, inner shell surface rough with many small translucent circular spots representing mantle attachment points and prominent radial grooves. Track of pallial blood vessel visible. Inner shell margin smooth.

Distribution.

50 - ca 150 m in offshore muds, northern Arabian Sea, Gulf of Oman, northeastern Arabian Gulf (Fig. 4). Smith (1906) records victorialis from the Arabian Gulf, 47 fthms, Investigator station 346, 26°37'30"N, 53°03'30"E.

Remarks.

This species is known only from shells. Scabrilucina victorialis is characterised by the deep cleft of the posterior sulcus and the fine, sharp, commarginal lamellae. Scabrilucina vitrea (see below) from off Sumatra and Gulf of Thailand is smaller, taller, and thinner shelled. The shell shape and the deep posterior sulcus superficially resemble some Thyasiridae such as Conchocele and this influenced Melvill’s initial placement in Cryptodon . Scabrilucina victorialis is also similar to Scabrilucina melvilli (new species below) from Australia that is distinguished by its smaller size, less deeply incised posterior sulcus and more widely spaced commarginal lamellae. Many of the shells of Scabrilucina victorialis from off Oman (MCZ 362493) and Scabrilucina vitrea from Thailand are penetrated by narrow, straight-sided holes ca 450 µm diameter (Figs 1A, C, 5E) comparable with those resulting from octopus predation ( Cortez et al. 1998, Todd and Harper 2010).