Microcystina striatula 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 : 33

Taxon classification Animalia Stylommatophora Ariophantidae

Microcystina striatula Vermeulen, Liew & Schilthuizen sp. n. Figure 26, 30

Microcystina striatula nomen nudum, Clements et al. 2008: 2761-2762.

Microcystina sp. “BO-02”, Schilthuizen and Vermeulen 2003: 96.

Holotype. Malaysia, Sabah, Tabin Valley ( RMNH.5003935 ).

Examined material from Sabah.

Interior Province. Crocker Range N.P., Gua Laing c. 12 km North of Keningau (leg. J.J. Vermeulen, V 1112). Gunung Trusmadi slopes: Gua Loloposon (leg. J.J. Vermeulen, V 13245). Pinangah valley, Batu Urun (= Bukit Sinobang) (leg. J.J. Vermeulen, V 1159). Pun Batu c. 30 km West of Sepulut (leg. J.J. Vermeulen, V 1287). Sepulut valley, Batu Punggul (leg. J.J. Vermeulen, V 1970); Batu Temurung (leg. M. Schilthuizen, BOR/MOL 730); Gua Pungiton (leg. J.J. Vermeulen & M. Schilthuizen, V 7550). Kudat Province. Banggi Island, South end (leg. J.J. Vermeulen, V 2515). Sandakan Province. Kinabatangan valley, Batu Materis (leg. M. Schilthuizen, BOR/MOL 1315); Batu Mawas (leg. T.S. Liew & M. Schilthuizen, BOR/MOL 2005); Batu Tomanggong Besar (leg. M. Schilthuizen, BOR/MOL 3611); Batu Tulug (Batu Putih) along road Lahad Datu-Sandakan, North of bridge over Kinabatangan River (leg. J.J. Vermeulen & H. Duistermaat, V 1499). Segama valley, North end of limestone ridge on East bank Tabin River (leg. J.J. Vermeulen & M. Schilthuizen, V 7779). Tawau Province. Batu Baturong c. 50 km W.S.W. Lahad Datu (leg. J.J. Vermeulen & H. Duistermaat, V 1854); North slope (leg. J.J. Vermeulen, V 7590). Gua Madai c. 40 km S.S.W. of Lahad Datu (leg. J.J. Vermeulen & H. Duistermaat, V 1723). Segama valley, hill N.W. of crossing road Sandakan-Lahad Datu with the Segama River (leg. J.J. Vermeulen & H. Duistermaat, V 1678); ‘Kirk’s Cave’ 8 km North of Lahad Datu (leg. J.J. Vermeulen, V 1228). Semporna area, Segarong Hills, Batu Tengar, 25 km E.S.E. of Kunak (leg. J.J. Vermeulen & H. Duistermaat, V 1822); Bukit Pababola, 25 km E.S.E. of Kunak (leg. J.J. Vermeulen & H. Duistermaat, V 1768); Bod Gaya Island (leg. T.S. Liew, Abdul & Ladja, BOR/MOL 4750); Sebangkat Island (leg. T.S. Liew & Abdul, BOR/MOL 4968). West Coast Province. Pulau Tiga in Kimanis Bay (leg. J.J. Vermeulen, V 11343). Kota Kinabalu, Kiansom (leg. UMS Tropical Malacology Course participants, BOR/MOL 3610).

Description.

Shell very small, thin, almost (slightly) translucent, white, lenticular; spire almost flat to slightly elevated. Surface with a silky luster. Whorls slightly to moderately convex. Protoconch with a very fine (hardly visible at 40 times magnification), densely placed, continuous, shallow, vaguely outlined spiral striation, and sometimes with fine, moderately spaced, shallow radial grooves towards the teleoconch only. Teleoconch with very fine (just visible at 40 times magnification) only slightly spaced, continuous, shallow, rather vaguely outlined spiral grooves on the upper surface; similar, but more densely placed grooves on the lower surface. This spiral sculpture is inconspicuous and patchy in some shells. Radial sculpture teleoconch: inconspicuous growth lines mainly, sometimes a few scattered, slight grooves. Umbilicus open, narrow, inner wall with an obtuse periomphalic edge; umbilical region distinctly concave. Dimensions: Height up to 1.1 mm; width up to 1.9 mm; diameters of the first three whorls 0.4-0.5 mm, 0.8-0.9 mm, 1.4-1.5 mm respectively; number of whorls up to 3 3/4; height aperture up to 0.8 mm; width aperture up to 1.0 mm.

Habitat in Sabah and distribution.

Rainforest, seasonally dry coastal forest and shrubby forest on limestone bedrock, up to 1000 m alt. Sabah: scattered localities; less common than Microcystina microrhynchus . Also in Kalimantan. Endemic to Borneo.

Cross diagnosis.

Differs at first sight from Microcystina microrhynchus by the presence of a fine spiral striation, giving the shell a soft, silky shine rather than a high gloss. Next to that, the umbilical area is more distinctly concave.

Elsewhere, Microcystina chionodiscus Vermeulen, 1996, from Bali, is similar, but Microcystina striatula has a more distinct spiral striation.

Remarks.

SEM images at 400 times magnification show that the areas in between the spiral grooves on the upper surface of the teleoconch have a ‘welded’ appearance.

Etymology.

The name refers to the sculpture [striatula (L.) = finely striated].