Ditropopsis tyloacron 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 : 13-15

Taxon classification Animalia Architaenioglossa Cyclophoridae

Ditropopsis tyloacron Vermeulen, Liew & Schilthuizen sp. n. Figure 12

Ditropopsis sp. “BO-02”, Schilthuizen et al. 2002: 257-258.

Holotype. Malaysia, Sabah, Tawau Province , Danum Valley Conservation Area ( RMNH5003920 ).

Examined material from Sabah.

Tawau Province. Danum Valley Conservation Area (leg. UMS students, V 9880, BOR/MOL 313).

Description.

Shell very small, rather thick, somewhat translucent, white to pale (yellowish) green. Surface shiny or glossy. Spire almost flat, but apex protruding, slightly oblique. Sculpture. Radial sculpture: fine growth lines, locally grading into fine, densely placed riblets. Spiral sculpture on the last whorl: 6 very distinct cords: 1 supraperipheral and 1 peripheral, the latter widest and widely projecting, 1 basal and 3 umbilical; next to these a fine spiral striation on the lower surface. Sculpture continuing up to the peristome, but close to the peristome distorted and partly obliterated by densely placed, low radial riblets and increasingly coarse spiral threads. Aperture. Peristome simple, not expanded, distinctly constricted in fully adult shells, parietal side attached to the penultimate whorl in fully adult shells, basal side angular, slightly to distinctly drawn out. Dimensions. Height 1.4-1.65 mm; width 2.5-2.8 mm; h/w 0.52-0.56; umbilicus measured over the basal spiral cord 33-37 % of the shell width; number of whorls c. 4; height aperture 0.7-0.9 mm; width aperture 0.8-0.9 mm.

Habitat in Sabah and distribution.

Primary forest on limestone soil, rarely on sandstone, 0-600 m alt. Sabah: S.E. part. Also in Kalimantan, East part. Endemic to Borneo.

Cross diagnosis.

Well characterized among Sabah Ditropopsis by the low, almost flat spire with only the apex protruding. In Kalimantan the Sabah form (illustrated) locally grades into series with relatively smooth, large shells and with the supraperipheral and umbilical ridges partly or entirely missing. Such shells look a little like Ditropopsis imadatei and Ditropopsis cincta , but have a flatter spire and a wider umbilicus.

Elsewhere, Ditropopsis moellendorfii Boettger, 1891 and Ditropopsis papuana E.A. Smith, 1897 have similarly flat shells, but the first has a double peristome, and the second a more rounded spire.

Etymology.

The name refers to the shape of the apex [tulos (Gr.) = knob; akros (Gr.) = at the top; a knobhead, therefore].