Rahula delopleura Vermeulen, Liew & Schilthuizen

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 : 90-91

Taxon classification Animalia Stylommatophora Euconulidae

Rahula delopleura Vermeulen, Liew & Schilthuizen sp. n. Figure 75

Rahula raricostulata auct. Schilthuizen and Vermeulen 2003: 96.

Rahula sp. V9667 auct. Clements et al. 2008: 2762.

Holotype. Malaysia, Sabah, Sandakan Province, Kinabatangan valley , Batu Pangi ( RMNH.5003927 ).

Examined material from Sabah.

Interior Province. Pinangah valley, Batu Urun (= Bukit Sinobang) (leg. J.J. Vermeulen, V 8006, BOR/MOL 827). Sepulut valley, Gua Pungiton (leg. J.J. Vermeulen & M. Schilthuizen, V 7556; leg. M. Schilthuizen, BOR/MOL 824); Batu Tinagas (leg. M. Schilthuizen, BOR/MOL 826); Gua Sanaron (leg. J.J. Vermeulen & M. Schilthuizen, V 8072). Sandakan Province. Kinabatangan valley, Batu Pangi (leg. J.J. Vermeulen & M. Schilthuizen, V 9667, BOR/MOL 2361); Batu Materis (leg. T.S. Liew & B. Elahan, BOR/MOL 2100); Batu Tomanggong Besar (leg. T.S. Liew & B. Elahan, BOR/MOL 2266, BOR/MOL 2299; leg. M. Schilthuizen, BOR/MOL 2360); Batu Tomanggong Kecil (leg. M. Salverda & H. van Oosten, BOR/MOL 2359). Segama Valley, North end of limestone ridge on East bank Tabin River (leg. J.J. Vermeulen & M. Schilthuizen, V 7787, BOR/MOL 825)). Tawau Province. Batu Baturong, North slope (leg. J.J. Vermeulen, V 7597). Gua Madai c. 40 km S.S.W. of Lahad Datu, N.E. end (leg. J.J. Vermeulen, V 7706). Segama valley, hill N.W. of crossing road Sandakan-Lahad Datu with the Segama River (leg. J.J. Vermeulen & H. Duistermaat, V 1676); ‘Kirk’s Cave’ 8 km North of Lahad Datu (leg. J.J. Vermeulen, V 1224); limestone hill on North bank Segama River, near bridge of road Sandakan to Lahad Datu (leg. J.J. Vermeulen, V 7512). Semporna area, Segarong Hills, Batu Tengar, 25 km E.S.E. of Kunak (leg. J.J. Vermeulen & H. Duistermaat, V 1820).

Description.

Shell small, rather solid, somewhat translucent to opaque, (pale) brown, conical with convex sides to almost ovoid; apex rounded. Surface shiny. Whorls convex, rounded, suture somewhat imperessed. Protoconch whorls convex, with very fine, densely placed radial riblets starting at some distance from the apex; apex with very fine (just visible at 40 times magnification), inconspicuous spiral striation, which gradually disappears where the radial riblets become more prominent. Teleoconch: Last whorl with a distinct spiral ridge slightly below the periphery, which seems to be the edge of a callus covering the lower surface of the shell, and which continues just above the suture of the penultimate whorl; next to this a fine, dense spiral striation on the lower surface of the shell. Radial sculpture above the spiral ridge consisting of well-spaced (26-33 on the last whorl), coarse, orthocline, approx. straight, high and narrow ribs, which reach down to the spiral ridge and are fused to it, interstices smooth or with an occasional, inconspicuous growth line. Umbilicus closed. Dimensions: Height up to 2.6 mm; width up to 2.1 mm; diameters of the first four whorls 0.5-0.6 mm, 0.8-0.9 mm, 1.1-1.2 mm, 1.35-1.55 mm respectively; number of whorls up to 6 1/2; height aperture up to 0.85 mm; width aperture up to 1.1 mm.

Habitat in Sabah and distribution.

Primary and secondary forest on limestone soil, up to 500 m alt. Sabah: Interior (Sepulut valley, upper Pinangah valley); East coast. Endemic to Sabah.

Cross diagnosis.

Differs from Rahula raricostulata (E.A. Smith, 1893) ( Sitala raricostulata E.A. Smith, 1893), from Sarawak, by the absence of a distinct, predominant spiral sculpture on the protoconch. Rahula raricostulata has a more conical spire, and fewer radial ribs (11-20) on the last whorl.

All continental Asiatic species of Rahula have prosocline radial ribs, see Blanford & Godwin Austen (1908: 249), and Godwin Austen (1918: 597).

Etymology.

The name refers to the sculpture [delos (Gr.) = manifest; pleura (Gr.) = rib].