Plectostoma margaretchanae, Marzuki & Liew & Mohd-Azlan, 2021

Marzuki, Mohammad Effendi bin, Liew, Thor-Seng & Mohd-Azlan, Jayasilan, 2021, Land snails and slugs of Bau limestone hills, Sarawak (Malaysia, Borneo), with the descriptions of 13 new species, ZooKeys 1035, pp. 1-113 : 1

Plectostoma margaretchanae sp. nov. Figures 12C , 13A-F

Material examined.

Holotype (SH 1.35 mm, SW 1.80 mm) (MZU.MOL.20.04), Malaysia, Sarawak, Kuching Division , Gunung Batu , limestone hill along Skio road, Jambusan, 2.4 miles E Bau, 1°23'50.65"N, 110°11'19.99"E, coll. M. E. Marzuki, 10.VII.2011 . Paratypes:> 10 ex. (ME0000227), same data as holotype ; 2 ex. (MZU.MOL.20.05),> 10 ex. (ME0000217), the same locality as holotype, coll. M. E. Marzuki, 11.III.2011 .

Differential diagnosis.

It differs other Bornean Plectostoma species by having a tiny shell, long projecting Plectostoma tuba free from the spire, and a constriction with a transverse palatalis and transverse basalis. It is most similar to P. pyrgiscus (Vermeulen, 1994) and P. tuba (Vermeulen, 1994) but P. pyrgiscus has a higher spire of six whorls with widely spaced radial ribs, while P. tuba also has higher spire without spiral striation, but with a double peristome.

Description.

Shell spire conical with slightly convex sides. Apex not or slightly oblique. Whorls 4½, convex; last whorl rounded. Constriction with a transverse palatalis, and a transverse basalis. Tuba free from the spire, long projecting, abruptly narrowed towards the constriction, rounded below. Teleoconch: radial ribs on spire moderately spaced (six ribs/0.5 mm on the penultimate whorl), not sinuous, those close to Plectostoma tuba not sinuous; those on Plectostoma tuba widely spaced (three ribs/0.5 mm half-way), not or hardly sinuous below. Spiral striation present, distinct. Aperture hardly tilted with regards to coiling axis, circular to elliptical, peristome simple, distant from the spire; slightly spreading. Umbilicus open, 0.13 mm across. Dimensions: spire height 1.25-1.35 mm; spire width 1.00 mm, shell width (including tube) 1.60-1.80 mm; aperture height and width 0.47 mm.

Geographic distribution and habitat.

Only known from the type locality. Living snails were observed foraging on the wet vertical limestone rock surfaces covered with mosses and lichens.

Etymology.

The specific epithet honours the Agronomist, Margaret Chan Kit Yok of Universiti Teknologi MARA, who was the mentor for the first author by providing valuable guidance for his malacological research in Sarawak.

Figures

Figure 12. A Plectostoma austeni (E. A. Smith, 1894) ME 8734 Lobang Angin B Plectostoma everetti (E. A. Smith, 1893) ME 8793 Gunung Batu C Plectostoma margaretchanae, sp. nov., MZU. MOL. 20.06 paratype Gunung Batu D Plectostoma wallacei busauense (E. A. Smith, 1893) ME 9495 Gunung Doya E Plectostoma wallacei teinostoma (Vermeulen, 1994) ME 8899 Gunung Doya F Plectostoma wallacei wallacei Ancey, 1887 ME 5898 Gunung Stulang.

Figure 13. Plectostoma margaretchanae sp. nov. A-C MZU. MOL. 20.04 holotype A Basal view B Apertural view C Abapertural view D-F ME 0227, paratypes D Basal view E-F Apertural view.