Taxon classification Animalia Archaeogastropoda Hydrocenidae

Georissa leucococca Vermeulen, Liew & Schilthuizen sp. n. Figure 19

Holotype. Malaysia, Sabah, Interior Province, Sepulut valley, Gua Pungiton (RMNH.5003956).

Examined material from Sabah.

Interior Province. Sepulut valley, Gua Pungiton (leg. J.J. Vermeulen & M. Schilthuizen, V 8081, BOR/MOL 61); Gua Sanaron (leg. J.J. Vermeulen & M. Schilthuizen, V 8068). Tawau Province. Gua Madai c. 40 km S.S.W. of Lahad Datu (leg. J.J. Vermeulen & H. Duistermaat, V 1736).

Description.

Shell minute, rather solid, translucent, white; spire conical with convex sides to approx. ovoid; apex rounded. Surface with a silky luster. Whorls moderately convex, rounded; last whorl somewhat more narrowly rounded to slightly angular at the periphery, rounded below. Protoconch minutely rugulose. Teleoconch: radial sculpture consisting of growth lines, locally grading into low, thin riblets at irregular intervals. Spiral sculpture: rather distinct, somewhat spaced, fine, low, thin, rounded spiral threads, on the last whorl present above the periphery, but absent in a narrow area just below the suture. Aperture semi-elliptic, with the parietal side approx. straight or slightly convex; peristome widely extended on the parietal side, not reflected elsewhere, free on the columellar side. Umbilicus open, rimate, a narrow slit underneath the reflected columellar peristome. Dimensions: Height 0.70-1.05 mm; width 0.65-1.00 mm; number of whorls 2 1/4-3; height aperture 0.35-0.50 mm; width aperture 0.35-0.45 mm.

Habitat in Sabah and distribution.

Primary and secondary forest on limestone bedrock. Alt. up to c. 500 m. Sabah: infrequent, a few localities only. Also in Sarawak. Endemic to Borneo.

Cross diagnosis.

The small size, hardly over 1 mm high at 3 whorls, characterizes the species. Georissa gomantongensis E.A. Smith, 1893, has a similar spiral sculpture. Apart from being larger, it has orange to yellow shells and a nodular uppermost spiral thread, situated close to the suture.

The name refers to the white shell [leucos (Gr.) = white; coccos (Gr.) = kernel].