Geotrochus labuanensis (Pfeiffer, 1863)

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 : 101-102

Taxon classification Animalia Stylommatophora Trochomorphidae

Geotrochus labuanensis (Pfeiffer, 1863) Figure 83

Helix labuanensis Pfeiffer, 1863: 523. Nanina conicoides (Metcalfe) var. labuanensis (Pfeiffer) Tryon, 1886: 48. Geotrochus labuanensis (Pfeiffer) Solem, 1964: 27. Type from Malaysia, Sabah, Labuan.

Examined material from Sabah.

Interior Province. Crocker Range N.P., Gua Laing c. 12 km North of Keningau (leg. J.J. Vermeulen, V 1105). Sepulut valley, Batu Punggul (leg. J.J. Vermeulen, V 1980); Batu Temurung (leg. J.J. Vermeulen, V 8053); Bukit Tinagas, East end of Batu Punggul limestone (leg. J.J. Vermeulen & M. Schilthuizen, V 7637); Gua Pungiton (leg. J.J. Vermeulen & M. Schilthuizen, V 7562; leg. M. Schilthuizen, BOR/MOL 901); Gua Sanaron (leg. J.J. Vermeulen & M. Schilthuizen, V 7670; leg. M. Schilthuizen, BOR/MOL 905; leg. T.S. Liew, M. Schilthuizen & S. Chiba, BOR/MOL 4281, BOR/MOL 4316). Sandakan Province. Kinabatangan valley, Batu Keruak (leg. T.S. Liew & B. Elahan, BOR/MOL 1848, BOR/MOL 1899); Batu Mawas (leg. T.S. Liew & M. Schilthuizen, BOR/MOL 1955); Batu Pangi (leg. J.J. Vermeulen & M. Schilthuizen, V 9676, BOR/MOL 2434); Batu Tai (not Bod Tai) near Gomantong (leg. J.J. Vermeulen & M. Schilthuizen, V 9601; leg. M. Schilthuizen, BOR/MOL 2436); Batu Tomanggong Besar (leg. T.S. Liew & B. Elahan, BOR/MOL 2283); Batu Tomanggong Kecil (leg. M. Salverda & H. Van Oosten, BOR/MOL 2437); Gomantong Cave (leg. A. van Til, BOR/MOL 3281). Segama valley, North end of limestone ridge on East bank Tabin River (leg. J.J. Vermeulen & M. Schilthuizen, V 7764, BOR/MOL 902); Tabin Wildlife Reserve (leg. M. Schilthuizen, BOR/MOL 904, BOR/MOL 906). Tawau Province. Batu Baturong c. 50 km W.S.W. of Lahad Datu (leg. J.J. Vermeulen & H. Duistermaat, V 1851); North slope (leg. J.J. Vermeulen, V 7602). Danum Valley (leg. H.A. Rutjes, BOR/MOL 903); Gua Madai c. 40 km S.S.W. of Lahad Datu, N.E.-end (leg. J.J. Vermeulen, V 7711). Segama valley, hill N.W. of crossing road Sandakan-Lahad Datu with the Segama River (leg. J.J. Vermeulen & H. Duistermaat, V 1656); ‘Kirk’s Cave’ 8 km North of Lahad Datu (leg. J.J. Vermeulen, V 1210); limestone hill on North bank Segama River, near bridge of road Sandakan to Lahad Datu (leg. J.J. Vermeulen, V 7518); Sabahmas Cave (leg. J.J. Vermeulen, V 7470).

Description.

Shell medium-sized, rather thin, opaque, creamy white, greyish very pale yellowish brown, periphery whitish, with a narrow, rather vaguely outlined, pale to dark (ochre-)brown band immediately above it, and often a second, similar band immediately below it, shell low-conical with approx. flat sides, apex not or hardly protruding. Surface shiny. Whorls: Inner whorls moderately convex, outer whorls flat to slightly convex; suture impressed in the inner whorls, not so in the outer, coinciding with the periphery; last whorl acutely angular, slightly compressed at the periphery, slightly convex below the periphery. Protoconch 2 1/8-2 1/2 whorls, smooth. Teleoconch. Radial sculpture: above and below the periphery scattered inconspicuous growth lines, locally grading into inconspicuous riblets. Spiral sculpture: last whorl with a sharp, slightly pinched peripheral ridge; start of fifth whorl with 4-25 usually well-spaced, low and thin spiral threads, the 2-5 threads close to the periphery more distinct, the others very inconspicuous or absent; no spiral sculpture below the periphery. Umbilicus closed. Peristome thickened and reflexed, basal edge most strongly curved towards the columellar side, and often, to a somewhat lesser extent, towards the periphery; in between only slightly curved. Dimensions: Height 6.3-7.6 mm; width 14.5-17.8 mm; h/w 0.39-0.45; peripheral keel of the last whorl at 0.44-0.54 of the shell height, measured from the apex; diameters of the first 4 whorls 1.3-1.6 mm, 2.2-2.7 mm, 3.6-4.4 mm, 5.2-7.0 mm respectively; number of whorls 6 1/8-6 7/8, height aperture 3.0-3.6 mm; width aperture 7.4-9.2 mm.

Habitat in Sabah and distribution.

Primary and secondary forest on limestone soil. Lives on decaying wood. Sabah: widespread, but scattered localities. More frequently found in the East part. Endemic to Sabah.

Cross diagnosis.

Differs mainly from Geotrochus kinabaluensis and Geotrochus oedobasis . by the presence of a peripheral colour band (not always present), the slightly pinched periphery, and the less convex outer whorls. The position of the peripheral keel relative to the shell height is intermediate between Geotrochus kinabaluensis and Geotrochus oedobasis . The spiral sculpture above the periphery is often more widely spaced, and more unequal, with a few stronger threads close to the periphery and very inconspicuous ones, if any, elsewhere.

Remarks.

Geotrochus labuanensis is a lowland species, contrary to the other species in the group.