Discartemon afthonodontia 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 : 68-70

15. Discartemon afthonodontia Siriboon & Panha sp. n. Figs 2E, F, 7A, B, 13 C–F, 19 A–E, 22D, 23, Table 2

Type material.

Holotype CUMZ 6249 (Fig. 7A). Measurement: shell height 4.8 mm, shell width 9.3 mm, and with 6½ whorls. Paratypes: CUMZ 4206 (1 shell), 6018 (4 shells), 6019 (23 shells), 6210 (7 specimens in ethanol; Figs 2E, 13 C–F, 19 A–E, 22D), NHMUK 20130677 (2 shells), and SMF (2 shells) from the type locality.

Other material examined.

Wat Khao Pho, Bang Saphan, Prachuap Khirikhan: CUMZ 6012, 6013. Wat Tam Khao Marong, Bang Saphan, Prachuap Khirikhan: CUMZ 4219, 6014, 6211 (5 specimens in ethanol). Bang Saphan Noi, Prachuap Khirikhan: CUMZ 3588. Tam Khao Phlu, Prathiew, Chumphon: CUMZ 3581, 3666, 6214 (3 specimens in ethanol; Figs 2F, 7B). Khao Maeo, Prathiew, Chumphon: CUMZ 3589. Nam Tok Kapo, Tha Sae, Chumphon: CUMZ 3593. Wat Tam Phru-Takien, Tha Sae, Chumphon: CUMZ 6016. Wat Uthai Tam, Chumphon: CUMZ 6212 (6 specimens in ethanol), 6261. Wat Tam Khwan Meuang, Sawi, Chumphon: CUMZ 6015. Suan Somdet, Lang Suan, Chumphon: CUMZ 6017. Tam Khao Krieb, Lang Suan, Chumphon: CUMZ 6213 (3 specimens in ethanol).

Type locality.

Tam Phitsadan, Prathiew, Chumphon, Thailand, 10°43'26.6"N, 99°15'23.6"E.

Diagnosis.

This new species can be distinguished from Discartemon plussensis , Discartemon leptoglyphus and Discartemon platymorphus in having a nearly smooth shell surface, a shouldered last whorl, and five to seven apertural lamellae. Discartemon afthonodontia sp. n. differs from Discartemon hypocrites by having a nearly smooth shell surface and an aperture with two parietal, two palatal, one basal and two columella lamellae. The genitalia of Discartemon afthonodontia sp. n. differ from those of Discartemon hypocrites in lacking a penial appendix, in having the free oviduct long and slender, and in having the vas deferens passing straight through the penial sheath. They also differ from Discartemon afthonodontia sp. n. in having conical penial papillae, long and slender penial hooks, and in having the penial wall with thick reticulated folds, and the vaginal wall with a smooth surface. Compared with Discartemon epipedis sp. n., Discartemon afthonodontia sp. n. has more apertural lamellae, lacks a penial appendix and has the vas deferens passing straight through the penial sheath. They also differ from Discartemon afthonodontia sp. n. in having a penial wall with thick reticulated folds, and in having a very long and slender free oviduct.

Description.

Shell. Shell depressed-heliciform, white and translucent; whorls 6, spire conical to convex with distinct suture. Shell surface glossy, smooth with transverse ridges near the peristome and varices present only on early whorls. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl shouldered, sometimes angular with strong peripheral keel, regularly expanded, and two shallow and short longitudinal furrows present. Umbilicus widely open and deep. Aperture sub-quadrangular; peristome discontinuous, thickened, expanded and reflected. Aperture dentition with one strong parietal, one palatal, one basal, one large columellar and one small supracolumellar lamella; sometimes upper parietal and upper palatal lamellae present (Fig. 7A).

Radula. Each row consists of 35-39 teeth with formula (17-19)-1-(17-19). Central tooth small with pointed cusp. Lateral and marginal teeth undifferentiated, unic uspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 22D).

Genital organs. Atrium (at) short. Proximal penis (p) short with very short, stout penial appendix (pa). Distal penis slender (Fig. 13D, E). Penial sheath (ps) thin, extending about one and half times penis length; penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 13C). Vas deferens (vd) passes straight through penial sheath before entering into penis distally (Fig. 13D). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.

Internal wall of atrium with numerous atrial pores (Fig. 19A). Penial wall with scattered brown penial hooks, about 5 hooks/200 µm 2 (Fig. 19B). Hooks located on conical penial papillae (pp) which are separated by thickened reticulated folds. Penial hooks small (<0.01 mm in length), expanded at base, tips pointed and curved towards genital orifice (Fig. 19C, D).

Vagina (v) short, about half of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) a very long and slender tube; oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small and slender. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 13C).

Vaginal wall surface generally smooth (Fig. 19E).

Etymology.

The specific epithet “afthonodontia” is derived from the Greek “afthonos” meaning “plenty” and “dontia” meaning “teeth”.

Distribution.

This species is known from several limestone karsts in Chumphon and Prachuap Khirikhan Provinces, southern Thailand. This is a narrow range confined to the Isthmus of Kra area, from 9° to 11° N and 99° to 100° E.

Remarks.

Shell variations are detected across populations. In the Tam Khao Phlu (CUMZ 3581, 3666, 6214) and Khao Maeo (CUMZ 3589) populations, shells have a stronger peripheral keel, a subcircular aperture, and lack the upper parietal lamella (Fig. 7B). The specimens from Wat Tam Khao Marong (CUMZ 4219, 6014, 6211), Wat Tam Khwan Meuang (CUMZ 6015), and Suan Somdet (CUMZ 6017) exhibit a convex spire, and the upper parietal and upper palatal lamellae are sometimes absent. However, these five populations exhibit similar genitalia characters including the penial sculpture. Therefore, we consider them all conspecific.