Discartemon roebeleni ( Moellendorff , 1894)

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 : 75-78

19. Discartemon roebeleni ( Moellendorff, 1894) Figs 3C, 8 B–G, 15 A–C, 20 A–E, 22E, 23, Table 3

Streptaxis roebeleni Möllendorff, 1894: 147, pl. 16, figs 3, 4. Type locality: Samui Island, Gulf of Siam. Gude 1903: 226. Gude 1920: 53. Laidlaw 1933: 233.

Odontartemon (Discartemon) roebeleni - Kobelt 1906: 99, pl. 54, figs 10, 11. Kobelt 1910: 150.

Discartemon roebeleni - Benthem Jutting 1954: 79, 81, fig. 3. Benthem Jutting 1959: 168. Zilch 1961: 82, pl. 5, fig. 4. Richardson 1988: 184. Maassen 2000: 88. Hemmen and Hemmen 2001: 42.

Material examined.

Lectotype of Streptaxis roebeleni SMF 108526 (Fig. 8B), and paralectotypes SMF 108527 (5 shells), 108528 (2 shells), 108529 (1 shell), 108530 (1 shell).

Holotype of forma major SMF 108531 (Fig. 8C), and paratype 108532 (2 shells). Holotype of forma minor SMF 108533 (Fig. 8D).

Topotypes from Samui, Thailand: NMW 1955.158.25255 (1 shell), and Nam Tok Hin Lad, Samui, Suratthani, Thailand, 9°31'15.3"N, 99°57'20.1"E: CUMZ 3655 (Fig. 8E), 4217, 6217 (52 specimens in ethanol; Figs 3C, 15 A–C, 20 A–E, 22E).

Topotypes from Samui, Thailand: NMW 1955.158.25255 (1 shell), and Nam Tok Hin Lad, Samui, Suratthani, Thailand, 9°31'15.3"N, 99°57'20.1"E: CUMZ 3655 (Fig. 8E), 4217, 6217 (52 specimens in ethanol; Figs 3C, 15 A–C, 20 A–E, 22E). Samui Island, Gulf of Siam [Thailand]: NHMW 36538 (1 shell), NHMW Rusnov R284 (1 shell), RMNH Fulton Coll. Reg. 177 (2 shells), ZMB 43127 (2 shells). Kow Tao Is. [=Ko Tao], Thailand: NMW 1955.158.25254 (7 shells). Ko Tao, Suratthani: CUMZ 3577. Ko Wuatalub, Ang Thong National Park, Suratthani: CUMZ 6022, 6218 (1 specimen in ethanol). Ko Mae Ko, Ang Thong National Park, Suratthani: CUMZ 6219 (1 specimen in ethanol). Ban Ta Khun, Suratthani: CUMZ 3590. Ratchaprapha reservior, Ban Ta Khun, Suratthani: CUMZ 6220 (4 specimens in ethanol). Khlong Saeng Wildlife Sanctuary, Ban Ta Khun, Suratthani: CUMZ 3652. Wat Khao Khok, Wiang Sa, Suratthani: CUMZ 3658. Wat Na San, Ban Na San, Suratthani: CUMZ 3578. Km 3, Khiri Rat Nikhom, Suratthani: CUMZ 6221 (1 specimen in ethanol). Wat Khao Phanom Wang, Suratthani: CUMZ 6222 (1 specimen in ethanol). Tam Hong, Khao Nan National Park, Nakhon Si Thammarat: CUMZ 4221. Tam Luang, Khao Nan National Park, Nakhon Si Thammarat: CUMZ 4231. Tam Phannara, Nakhon Si Thammarat: CUMZ 3667. Tam Khun Klung, Nopphitam, Nakhon Si Thammarat: CUMZ 6021. Khao Phrathong, Cha-uat, Nakhon Si Thammarat: CUMZ 3599. Wat Suwankhuha, Takua Thung, Phangnga: CUMZ 3661 (Fig. 8F), 6223 (14 specimens in ethanol). Sra Morakot, Krabi: CUMZ 6023, 6226 (7 specimens in ethanol). Ao Phra Nang, Krabi: CUMZ 3651. Khao Huai Hang, Huai Yot, Trang: CUMZ 3656. Tam Lay-Kao Krop, Huai Yot, Trang: CUMZ 3600. Botanic Garden, Trang: CUMZ 3663. Khao Pi-na, Na Yong, Trang: CUMZ 6024. Tam Sumno, Trang: CUMZ 6225 (1 specimen in ethanol). Khao Pu-Khao Ya National Park, Si Banphot, Phatthalung: CUMZ 3575, 3596. Tam Wang Thong, Phatthalung: CUMZ 3662, 6027, 6224 (6 specimens in ethanol). Wat Khaotupson, Phatthalung: CUMZ 3678. Khao Ok Thalu, Phatthalung: CUMZ 3595. Khao Chaison, Phatthalung: CUMZ 6028. Tam Tanan, Satun: CUMZ 6025. Tam Khantiphon, Satun: CUMZ 6026, 6227 (1 specimen in ethanol). Ko Buloan Pai, La Ngu, Satun: CUMZ 3591. Ko Tarutao, Satun: CUMZ 6228 (7 specimens in ethanol), 6256 (Fig. 8G). Ko Klang, Tarutao, Satun: CUMZ 6229 (9 specimens in ethanol). Khao Nui, Rattaphum, Songkhla: CUMZ 3598.

Description.

Shell. Shell globose-heliciform, white and translucent; whorls 6 –6½, spire conical with distinct suture. Shell surface glossy, with transverse ridges that diminish below periphery; varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl rounded, regularly expanded; umbilicus widely open and deep. Aperture sub-quadrangular; peristome discontinuous, thickened, expanded and reflected. Apertural dentition with one strong parietal, one palatal, one basal and one columellar lamella (Fig. 8B). Sometimes basal lamella absent (Fig. 8F), or upper palatal and supracolumellar lamellae present (Fig. 8G).

Radula. Each row consists of 21-33 teeth with formula (10-16)-1-(10-16). Central tooth very small and triangular with a pointed cusp. Lateral and marginal teeth undifferentiated, unicuspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 22E).

Genitalia organs. Atrium (at) long. Penis short and slender. Penial sheath (ps) extending entire penis length; penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 15A). Vas deferens (vd) passes through about one-seventh of penial sheath length before entering into penis distally (Fig. 15B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.

Internal wall of atrium generally corrugated (Fig. 20A). Penial wall with scattered, transparent penial hooks, about 8 hooks/200 µm 2. Hooks located on very short penial papilla (pp). Penial hooks small (<0.03 mm in length), short, expanded at base, tips pointed and curved towards genital orifice (Fig. 20C, D).

Vagina (v) short, about half of penis length. Gametolytic duct (gd) a long and slender tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) short, about same length as vagina; oviduct (ov) folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, very short. Hermaphroditic duct (hd) bearing extremely long seminal vesicle (sv) (Fig. 15C).

Vaginal wall generally with longitudinal vaginal folds (Fig. 20E).

Distribution.

This species is found in limestone habitats and is common in southern Thailand. The geographic distribution records are in eight Provinces, ranging from 10°N to 6°N: Suratthani, Nakhon Si Thammarat, Krabi, Phangnga, Phatthalung, Trang, Satun, and Songkhla.

Remarks.

Discartemon roebeleni can be distinguished from Discartemon collingei by its rounded, regularly coiled last whorl and wider umbilicus. It differs from Discartemon stenostomus in the higher spire with transverse ridges that diminish below the periphery, a sub-quadrangular aperture, and in having a basal lamella.