Discartemon tonywhitteni Sutcharit & Panha, 2020

Figs 1, 2A, 3A, B, 4A, B, 5, 24A

Discartemon tonywhitteni Sutcharit & Panha in Sutcharit et al. 2020: 154, fig. 3a-c. Type locality: Phra (Buddha) Cave, Lenya National Park, Tanintharyi Township, Tanintharyi Region, Myanmar.

Material examined.

Holotype CUMZ 5108; paratypes CUMZ 5107 (14 shells), CUMZ 5101 (30 shells), CUMZ 5102 (25 shells), CUMZ 5104 (18 shells), CUMZ 5105 (30 shells), CUMZ 5106 (20 juvenile shells). Limestone outcrop ~ 3.4 km south of the Phra (Buddha) Cave, Lenya National Park, Tanintharyi Township, Tanintharyi Region, Myanmar (11°11'56.2"N, 99°10'25.7"E): CUMZ 13001 (7 specimens in ethanol; Fig. 3A, B).

Diagnosis.

This species was clearly described in Sutcharit et al. (2020). Shell is depressed-heliciform, white and translucent, spire low conical to convex with wide and depressed suture. Shell surface glossy, with fine transverse ridges that diminish below periphery; varices present. Embryonic shell large, ~ 2½ whorls with smooth surface; following whorls in regularly expanding coil. Last whorl usually angular; widely open umbilicus. Apertural dentition with one strong parietal, one palatal, one basal, one columellar and one supracolumellar lamella (Fig. 3A, B).

Genital organs. Atrium (at) short. Penis (p) long and slender. Penial sheath (ps) thin and extending ~1/2 to 3/4 of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting distally on penial sheath (Fig. 4A). Vas deferens (vd) very short, ~ 1/6 of penial sheath length and passes through penial sheath before entering penis distally (Fig. 4B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.

Internal wall of atrium generally smooth (Fig. 5A). Proximal and middle penial wall with dense and translucent penial hooks (~ 5 hooks/200 μm 2) and located on conical papillae (Fig. 5B-D). Penial hooks small (<0.04 mm in length), expanded at base, tips pointed (Fig. 5C, E). and curved towards genital orifice. Most penial hooks with blunt tips (Fig. 5E). Distal penial wall with dense and translucent conical penial papillae with embedded penial hooks, ~ 12 penial papillae/200 μm 2 (Fig. 5F).

Vagina (v) short, ~ 1/3 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) long, ~ 2 times of vagina length. Oviduct (ov) slender and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) ca. twice as long as the length from talon to branching point of seminal vesicle (Fig. 4A).

Vaginal wall with transverse vaginal folds; vaginal hook absent (Fig. 5G).

Radula . Each row consists of ~ 35-49 teeth with formula (24-17) -1- (17-24). Central tooth very small with pointed cusp. Lateral and marginal teeth undifferentiated, unicuspid and lanceolate. Latero-marginal teeth gradually reducing in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 24A).

Distribution.

Discartemon tonywhitteni is the southernmost distributed species and, currently, is known as the only form from the type locality (Fig. 1), which is an isolated limestone outcrop in Tanintharyi Region, southern Myanmar (Sutcharit et al. 2020).

Remarks.

Sutcharit et al. (2020) described D. tonywhitteni based only on shells. Fortunately, seven alcohol-preserved specimens collected near the type locality were sent by the FFI staff after the species was published. These additional specimens allow us to describe the genitalia and radular morphology of this species herein.