Discartemon circulus 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 : 60-61

8. Discartemon circulus Siriboon & Panha sp. n. Figs 5C, D, 23, Table 1

Type material.

Holotype CUMZ 6246 (Fig. 5C). Measurement: shell height 3.9 mm, shell width 7.7 mm, and with 6 whorls. Paratypes: CUMZ 3665 (9 shells), 6262 (8 shells), NHMUK 20130674 (2 shells), and SMF (2 shells) from the type locality.

Type locality.

Tam Phannara, Nakhon Si Thammarat, Thailand, 8°25'18.8"N, 99°22'46.8"E.

Diagnosis.

Discartemon circulus sp. n. differs from Discartemon discus and Discartemon sykesi in its narrower umbilicus, sub-quadrangular aperture, and apertural dentition with five lamellae. In addition, Discartemon discus has a larger shell, while Discartemon sykesi has an intermediately expanded last whorl and a sinulus. Compared with Discartemon khaosokensis , Discartemon circulus sp. n. has a smaller shell, a flattened spire with weak transverse ridges, an angular last whorl, a sinulus, and five apertural lamellae. Discartemon circulus sp. n. differs from Discartemon discadentus sp. n. and Discartemon discamaximus sp. n. in having a smaller shell with weak transverse ridges and five apertural lamellae. Compared with Discartemon expandus sp. n., Discartemon circulus sp. n. has weaker transverse ridges, a regularly expanded peristome, and five apertural lamellae.

Description.

Shell. Shell flattened, white and translucent; whorls 5½– 6, spire flattened, with a distinct suture. Shell surface glossy with weak transverse ridges and varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, regularly expanded; umbilicus very wide, deep and showing all preceding whorls. Aperture sub-quadrangular; peristome discontinuous, thin and expanded. Apertural dentition with one parietal, one palatal, one small basal, one small columellar and one small supracolumellar lamella (Fig. 5C).

Etymology.

The specific epithet is from the Latin “circulus” meaning “circle”. It refers to the appearance of this new species when seen from the apex.

Distribution.

This species is known only from the type locality, an isolated limestone hill which reaches about 200 meters amsl, about 20 km southwest of Tai Rom Yen National Park.

Remarks.

Apparently rare and extensive searching revealed no living examples.