Discartemon Pfeiffer, 1856

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 : 47-48

Genus Discartemon Pfeiffer, 1856

Discartemon Pfeiffer, 1856: 173. Ancey 1884: 399. Tryon 1885: 58. Gude 1903: 226. Benthem Jutting: 1954: 71-94. Zilch 1960: 560. Richardson 1988: 182-185: Schileyko 2000: 784. Hemmen and Hemmen 2001: 42.

Odontartemon (Discartemon) - Kobelt 1905-1906: 91, 96.

Type species.

Streptaxis discus Pfeiffer, 1853, by subsequent designation by Ancey (1884: 399).

Description.

Shell. Shell flattened to globose-heliciform, white, semi-transparent to translucent. Whorls 4-7; spire flattened to conical. Shell surface glossy, nearly smooth or with transverse ridges; varices often present. Embryonic shell, about 2½ whorls, with a smooth surface; following whorls regularly coiled or at most only slightly axially deflected. Last whorl rounded to angular, often with peripheral keel, whorls regularly to rapidly expanded. Umbilicus open to very widely open. Aperture semi-ovate to triangular. Peristome discontinuous, thin to thick, expanded and reflected. Longitudinal furrows outside aperture may be present. Apertural dentition always with one parietal lamella; other lamellae may be present including: upper palatal, palatal, basal, columellar and supracolumellar lamellae.

Radula. Teeth unicuspid, elongate lanceolate, and arranged in anteriorly V-shaped rows. Central tooth tiny with pointed cusp. Lateral and marginal teeth undifferentiated. Latero-marginal teeth gradually reduce in size, with outermost teeth smaller and shorter than inner teeth.

Genital organs. Penis short to long, sometimes with a penial appendix. Penial sheath short (less than half of penis length) to long (equivalent to penis length). Internal wall of introverted penis with transparent to brown penial hooks. Vas deferens passes through a short section of penial sheath before connecting distally to penis. Vagina and free oviduct short to long. Seminal vesicle present, convoluted, short to long.

External features. Live specimens exhibit a semi-transparent dark yellow to pale yellow body, covered with reticulated skin, and sometimes with brownish spots. Upper tentacles long with black eye-spot on the tip, yellow to orange; lower tentacles short. Brownish digestive gland and black kidney may be visible through transparent shell. Foot narrow, undivided and with short tail.

Remarks.

The genitalia of Discartemon are distinguished from those of other Southeast Asian streptaxid genera in sometimes having a penial appendix, in lacking vaginal hooks, and also as follows: Indoartemon has the vas deferens attached to the distal end of the penial sheath by a narrow band of connective tissue; in Perrottetia the gametolytic duct and sac may not extend as far as the albumin gland; and Haploptychius and Oophana have a long penial sheath and very short seminal vesicle respectively ( Stoliczka 1871, Berry 1963, 1965, Schileyko 2000, Siriboon et al. 2013, Siriboon et al. in press).

An identification key to species follows. In addition we propose an informal subdivision of Discartemon into three groups of species, based mainly on shell shapes as shown in Figure 1, that may be useful as an alternative aid to identification. The figures of shells are presented in the same order.

Further remarks on the systematics and biogeography of the genus are made in the Discussion.

Group I: Discartemon discus -group. Have a generally flattened shell with a concave to flattened spire, and a very wide umbilicus. The H/W ratio ranges between 0.3-0.5 (average 0.40). This group comprises 10 species: Discartemon discus (Pfeiffer, 1853), Discartemon planus (Fulton, 1899), Discartemon sykesi (Collinge, 1902), Discartemon nummus (Laidlaw, 1929), Discartemon khaosokensis Panha & Burch, 1998, Discartemon circulus sp. n., Discartemon discadentus sp. n., Discartemon discamaximus sp. n., Discartemon deprima sp. n., and Discartemon expandus sp. n.

Group II: Discartemon plussensis -group. Have a depressed-heliciform shell with a flattened to only slightly convex spire, and a widely open umbilicus. The H/W ratio ranges between 0.4-0.6 (average 0.50). This group comprises 7 species: Discartemon plussensis (Morgan, 1885), Discartemon hypocrites Benthem Jutting, 1954, Discartemon leptoglyphus Benthem Jutting, 1954, Discartemon platymorphus Benthem Jutting, 1954, Discartemon afthonodontia sp. n., Discartemon epipedis sp. n., and Discartemon flavacandida sp. n.

Group III: Discartemon roebeleni -group. Have a globose-heliciform shell with a conical to elevated conical spire, and a widely open umbilicus. The H/W ratio ranges between 0.5-0.8 (average 0.63). This group comprises 10 species: Discartemon lemyrei (Morlet, 1883), Discartemon roebeleni ( Möllendorff, 1894), Discartemon collingei (Sykes, 1902), Discartemon stenostomus Benthem Jutting, 1954, Discartemon sangkarensis Benthem Jutting, 1959, Discartemon vandermeermohri Benthem Jutting, 1959, Discartemon conicus sp. n., Discartemon kotanensis sp. n., Discartemon megalostraka sp. n., and Discartemon triancus sp. n.