Vesicomya prashadi Hoffman & Little, 2025

Vesicomya prashadi Hoffman & Little sp. nov.

Fig. 17B–D View Fig .

Zoobank LCID: urn:lsid:zoobank.org:act:8D92F14F-BB4A-41D9-92BF-F326FA809A7F .

Etymology: After Baini Prashad (1894–1969), Indian malacologist, particularly known for his study of the deep-water bivalves from the Siboga expedition ( Prashad 1932).

Type material: Holotype, one shell, SMF373074 About SMF . Paratypes, one valve, SMF373072 About SMF ; one valve, SMF373073 About SMF , from the type locality and horizon .

Type locality: Northern Indian Ocean, Krishna-Godavari Basin , Bay of Bengal, offshore eastern India, 15°51.6335’ N, 81°50.2274’ E, 1046 m water depth GoogleMaps .

Type horizon: 16.38–16.88 mbsf level, core NGHP-01-12A; Upper Pleistocene .

Material.— Type material and several specimens from core NGHP-01-12A (for details see Table 1).

Diagnosis.—Small, solid, smooth, equivalve, inequilateral shell with oval outline, convex on all sides, beaks anteriorly, demarcated lunule and escutcheon, smooth prodissoconch.

Dimensions.— Holotype height 5.0 mm, length 6.0 mm, tumidity 4.2 mm. Maximum dimensions of shells in type set height as in holotype.

Description.—Prodissoconch single stage evident only, subcircular, truncated dorsally, flattened, smooth. Transition to dissoconch clear by change in sculpture. Length 300 μm. Dissoconch widely convex with prosogyrous umbos at 30% from anterior end; moderately inflated. Posterio-dorsal margin straightened, slightly convex, obliquely truncated posteriorly; ventral margin widely convex; anterior most convex; anterio-dorsal margin with indent at lunule; external sculpture with numerous fine growth margins of variable strength. Long lanceolate escutcheon, with fine growth lines, large lanceolate area for external ligament. Large triangular lunule with indented margins, with somewhat regular coarse growth lines. Ventral margin sharp, dorsal margin blunt. Internally surface and internal margin smooth; muscle scars and pallial line inconspicuous. Adductor scars of equal size; pallial line with minor sinus. Hinge only known from left valve; one curved elongated tooth posterior of umbo, elongated cavity for tooth right valve below; a second inverted w-shaped tooth below umbo, a short cavity for tooth right valve below posterior end w-tooth; one weak lateral tooth below posterio-dorsal margin; no anterior lateral tooth.

Remarks.—The genus Vesicomya has been based on the morphology of dentition in the left valve. The proximal curved tooth and the, long, more distal flexuous tooth Vesicomya prashadi Hoffman & Little sp. nov. is most similar to the dentition in the type species Vesicomya atlantica ( Krylova et al. 2018: fig. 2C: teeth 2a, b, 4b) or that of the congener Vesicomya alleni ( Krylova et al. 2018: fig. 3D). The type species of Vesicomya has a thin shell and narrow hinge plates whereas Vesicomya prashadi Hoffman & Little sp. nov. has a thick shell and heavy hinge plates. Vesicomya alleni has nearly identical teeth and hinge plate in the left valve but its shell is more elongated and the umbo is located further to the anterior ( Krylova et al. 2018). Vesicomya prashadi Hoffman & Little sp. nov. has a more elevated outline and its umbos are in a nearly central position. Vesicomya indica ( Knudsen, 1970) is known from abyssal depths in the Bay of Bengal ( Huber 2010). That species has similar teeth compared to Vesicomya prashadi sp. nov but its hinge plate is narrower, its triangular outline is more elevated (height/ length ±1) and the lunule is rounded. The escutcheon is also less pronounced; the co-marginal sculpture is fine and regular. Vesicomya prashadi Hoffman & Little sp. nov. is more flattened with a more triangular lunule, a pronounced escutcheon, an elongate-oval outline and a more irregular growth sculpture.

We considered placement of Vesicomya prashadi Hoffman & Little sp. nov. in other genera of small vesicomyids, for example Waisiuconcha Beets, 1942 , and Isorropodon Sturany, 1896 . Waisiuconcha was rejected as the dentition of the type species Waisiuconcha alberdinae Beets, 1942 , are clearly different ( Beets 1942: figs. 147–148: thick strong teeth). The same character is observed in, for example, the Atlantic Waisiuconcha haeckeli Cosel & Salas, 2001 Zettler and Hoffman 2021 : figs. 4, 12). We also rejected placement in Isorropodon because species in this genus have elongated, dorsally aligned teeth, as in evident in the original illustrations of the type species Isorropodon perplexum Sturany, 1896 ( Sturany 1896: pl. 1: 24–27).

Stratigrapic and geographic range.— Type locality and horizon only.