Angulyagra oxytropis ( Benson, 1836 )

Angulyagra oxytropis ( Benson, 1836) View in CoL

Fig. 4 View Fig

Paludina oxytropis Benson, 1836: 745 View in CoL ( type locality not stated in the original description).

Paludina pyramidata von dem Busch, 1844 View in CoL in Philippi 1842 –1850: 113, pl. 1 figs 3–4.

Vivipara oxytropis View in CoL – Preston 1915: 84. — Annandale & Seymour Sewell 1920: 113. — Annandale 1921: 544–552, figs 2–5.

Dactylochlamys oxytropis View in CoL – Rao 1925: 132.

Angulyagra oxytropis View in CoL – Rao 1931: 301. — Subba Rao 1989: 51, fig. 70. — Preece et al. 2022: 94, fig. 38a.

Diagnosis

Shell large, fragile and lightweight. Each teleoconch whorl with three strong keels, open umbilicus bordered by one strong keel. Operculum with growth lamellae on exterior surface and radial striae on interior surface. Inner and outer marginal teeth of radula both nearly half of lateral tooth in width. Mantle edge with a number of finger-shaped processes.

Material examined

Holotype

BENGAL • dry preserved specimen; NHMUK.1879.12.26.120 .

Other material

INDIA • 8 specs (preserved dry, 6 adults and 2 juveniles); Manipur, Loktak “ Logtak Lake ”; NHMUK.1974.03.7.1 to NHMUK. 1974.03.8 • 2 specs (preserved dry); Assam, Manipur, Loktak Lake ; NHMUK. 2019.04.31 .

Description

Shell ( Fig. 4A–F View Fig ) large, broadly conical, thin, lightweight, fragile, olive to greenish brown; up to six whorls at adulthood, including one relatively smooth protoconch whorl, apex acute; each teleoconch whorl with three strong primary keels of darker colour, the strongest keel above suture, one to two weaker smooth secondary keels located between primary keels; base of shell with three to four spiral keels of darker colour, one to two weaker secondary keel located between strong primary keels; aperture ovate, inner shell surface bluish white, with obvious grooves corresponding to the position of the three strong keels, outer lip thin, three strong keels extending to margin of outer lip, columellar lip thin and simple; umbilicus broadly open, bordered by a strong keel.

Operculum ( Fig. 4G–H View Fig ) corneous, transparent pale brown, rather thin; nucleus sub-central, close to inner margin; exterior surface with regularly distributed growth lamellae; interior surface with large inner opercular region and radial striae starting from nucleus; nuclear region relatively large, smooth and glossy, with veins at margin.

Radular central tooth with one broad central denticle and five small sharp cusps on either side; lateral tooth with one broad central denticle, three small sharp cusps on inner side and six small sharp cusps on outer side; inner and outer marginal teeth narrow, both nearly half of lateral tooth in width; inner marginal tooth with one broad central denticle and three small sharp cusps on either side; outer marginal tooth with 15 tiny sharp cusps (summarized based on the figure and description from Annandale 1921).

Mantle edge with a number of finger-shaped processes, three of these processes larger, each large process corresponding to a groove of the inner shell surface; gill lamella with a broad base and a long finger-shaped part; about ten embryos and ten eggs in the uterus of a pregnant female (summarized based on the figure and description from Rao (1925) and Annandale (1921)).

Remarks

This species can be easily distinguished from the other viviparid species according to the remarks for the genus. As the type species of Angulyagra , A. oxytropis shows large morphological and anatomical differences to many species nominally assigned to Angulyagra , especially in the large, thin, light and fragile shell with an open umbilicus and simple columellar lip, the distinctive operculum, and marginal teeth of the radula.

Habitat and distribution

Loktak Lake and nearby wetland ponds in the Manipur Valley of India.