Thysanota grenvillei (Brazier, 1876)

Vermeulen, Jaap J., Liew, Thor-Seng & Schilthuizen, Menno, 2015, Additions to the knowledge of the land snails of Sabah (Malaysia, Borneo), including 48 new species, ZooKeys 531, pp. 1-139 : 62

Taxon classification Animalia Stylommatophora Endodontidae

Thysanota grenvillei (Brazier, 1876) Figure 51

Helix grenvillei Brazier, 1876: 104. Queridomus grenvillei (Brazier) Solem, 1988: 552. Type from Australia, Queensland, Cape York Peninsula.

Examined material from Sabah.

Tawau Province. Gua Madai c. 40 km S.S.W. of Lahad Datu (leg. J.J. Vermeulen & H. Duistermaat, V 1730). Semporna area, Segarong Hills, Batu Tengar, 25 km E.S.E. of Kunak (leg. J.J. Vermeulen & H. Duistermaat, V 1789); Bukit Pababola, 25 km E.S.E. of Kunak (leg. J.J. Vermeulen & H. Duistermaat, V 1775).

Description.

Shell very small, rather thin, somewhat translucent or opaque, (pale) brown, somewhat depressed conical with approx. flat sides; apex rounded. Surface about dull or with a silky luster above the periphery, shiny below. Whorls moderately convex, (moderately) angular at the periphery, above the periphery rounded or with a second, slight angle at a distance from the periphery, below the periphery rounded. Protoconch whorls convex, with 7-10 rather distinct, very fine, well-spaced, thin spiral threads; radial sculpture absent. Teleoconch: Last whorl with a distinct peripheral spiral thread coinciding with the suture of the penultimate whorl, above this 1(-2) less distinct threads as well as numerous very fine spiral threads, the latter more widely spaced towards the upper suture; below the peripheral thread a number of finer threads close to it, as well as a fine, continuous, moderately spaced striation over most of the lower surface. Radial sculpture: growth lines, above the periphery grading into densely placed, rather regularly spaced, fine, narrow riblets, which form minute nodes where they cross the spiral threads. Umbilicus open, narrow. Dimensions: Height up to 2.0 mm; width up to 2.5 mm; diameters of the first four whorls 0.4-0.5 mm, 0.70-0.95 mm, 1.15-1.50 mm, 1.85-2.40 mm respectively; number of whorls up to 4 5/8; height aperture up to 0.85 mm; width aperture up to 1.25 mm.

Habitat in Sabah and distribution.

Found on limestone hills near the coast. Elsewhere also found in coastal environments. Sabah: Gunung Madai, Segarong Hills E.N.E. of Semporna. Distribution elsewhere: Vietnam; Australia.

Cross diagnosis.

More depressed conical than Thysanota conula , with the shell wider than high.

Remarks.

The Borneo material is virtually identical with the Australian shell shown in Solem (1988: 552), and with material collected by the first author in Ha Long Bay, northern Vietnam. Australian shells have periostracal hairs where the more distinct spiral threads cross the radial ribs. In some Vietnam shells these hairs are fused to low, erose periostracal crests on the spiral threads. In the Borneo shells, all periostracum has worn off.

The species is now known from three widely distant coastal areas. It is probably a widespread element of the coastal fauna, but appears very rare. It is not an Australian endemic species, as was assumed so far.