Discartemon expandus Siriboon & Panha

Siriboon, Thanit, Sutcharit, Chirasak, Naggs, Fred, Rowson, Ben & Panha, Somsak, 2014, Revision of the carnivorous snail genus Discartemon Pfeiffer, 1856, with description of twelve new species (Pulmonata, Streptaxidae), ZooKeys 401, pp. 45-107 : 63-64

10. Discartemon expandus Siriboon & Panha sp. n. Figs 5G, H, 23, Table 1

Type material.

Holotype CUMZ 6248 (Fig. 5G). Measurement: shell height 3.8 mm, shell width 8.3 mm, and with 5½ whorls. Paratypes: CUMZ 3664 (10 shells), NHMUK 20130676 (2 shells), and SMF (2 shells) from the type locality.

Type locality.

Klong Hoy, Suratthani, Thailand, 8°57'18.1"N, 98°48'30.7"E.

Diagnosis.

Discartemon expandus sp. n. differs from Discartemon discus and Discartemon sykesi in its smaller shell with transverse ridges, intermediately expanded last whorl, and widely expanded peristome. In addition, a sinulus is absent in Discartemon discus . Discartemon expandus sp. n. can be distinguished from Discartemon khaosokensis by having a flattened spire, an angular and intermediately expanded last whorl, and a widely expanded peristome. Compared with Discartemon discadentus sp. n. and Discartemon discamaximus sp. n., Discartemon expandus sp. n. has a smaller shell with strong transverse ridges, a sinulus and a widely expanded peristome. Moreover, Discartemon discadentus sp. n. has five apertural lamellae, and Discartemon discamaximus sp. n. has a rapidly expanded last whorl.

Description.

Shell. Shell flattened, white and semi-transparent; whorls 5½– 6, spire flattened with a distinct suture. Shell surface glossy with transverse ridges that diminish below periphery; varices present. Embryonic shell large, about 2 –2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, intermediately expanded; umbilicus very wide, deep and showing all preceding whorls. Aperture semi-ovate with narrow sinulus; peristome discontinuous, thin and widely expanded. Apertural dentition of only one parietal lamella (Fig. 5G).

Etymology.

The specific epithet “expandus” is derived from the Latin “expandi” meaning “expand”. It refers to the expanded peristome of this species.

Distribution.

The species is known only from the type locality and extensive searching revealed no living examples.

Remarks.

Some variation has been observed in the spire, which is slightly convex rather than flattened in some specimens, and in the distinctness of the suture.