Discartemon paurodeviatus Man & Panha, 2022

Sian Man, Nem, Siriboon, Thanit, Lin, Aung, Sutcharit, Chirasak & Panha, Somsak, 2022, Revision of the carnivorous land snail family Streptaxidae (Stylommatophora, Achatinina) in Myanmar, with description of four new species, ZooKeys 1110, pp. 39-102 : 39

Discartemon paurodeviatus Man & Panha sp. nov.

Figs 1 , 2B , 3C-E , 4C, D , 6 , 24B

Type material.

Holotype CUMZ 13002 (Fig. 3C ). Measurements: shell height 7.6 mm, shell width 11.0 mm, and 6 whorls. Paratypes CUMZ 13003 (14 shells; Fig. 3D, E ), CUMZ 13004 (3 specimens in ethanol), NHMUK (2 shells), all from the type locality.

Type locality.

Small hill on Pahtaw Pahtet Island (~ 500 m west of Myeik Town), Myeik Township, Tanintharyi Region, Myanmar (12°26'3.5"N, 98°35'14.1"E).

Diagnosis.

Discartemon paurodeviatus sp. nov. can be distinguished from D. collingei (Sykes, 1902) from Malaysia by having a larger shell, rounded last whorl, semi-ovate and slightly reflected aperture, and sometimes supracollumellar lamellae are present. Compared with D. vandermeermohri van Benthem Jutting, 1959 and D. mekalostraka Siriboon & Panha, 2014 from Thailand, this new species has a slightly extended last whorl from the penultimate whorl, last whorl slightly axially deflected, widely open umbilicus, and semi-ovate aperture. The genital organs of D. paurodeviatus sp. nov. differ from D. mekalostraka by having corrugated atrium without pore, short penis, dense brownish and long slender penial hooks located on penial papillae, and short vagina with thickened and reticulated vaginal folds.

Description.

Shell globose-heliciform, white and translucent; whorls 6- 6½; spire conical with distinct suture. Shell surface glossy with fine transverse ridges that diminish below periphery; varices present. Embryonic shell ~ 2½ whorls with smooth surface; following whorls regularly coiled. Last whorl rounded, little axially deflected and extruded from the penultimate whorl. Aperture semi-ovate; peristome yellowish to whitish, discontinuous, thickened, expanded, and slightly reflected. Apertural dentition with one strong parietal, one small palatal, one large basal, and one small columellar lamella; sometimes with small supracolumellar lamellae. Umbilicus open and deep (Fig. 3C-E ).

Genital organs. Atrium (at) short. Penis (p) long and slender. Penial sheath (ps) very thin, extending entire penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting distally on penial sheath (Fig. 4C ). Vas deferens (vd) passes through penial sheath without insertion before entering penis distally (Fig. 4D ). Penial retractor muscle (pr) thin and long, inserting at penis and vas deferens junction.

Internal wall of atrium corrugated with sparse atrial pores (Fig. 6A ). Penial wall with scattered, very long, slender, and pale brown penial hooks (~ 10 hooks/200 μm 2), hooks located on conical papillae that are separated by distinct reticulated folds (Fig. 6C, D ). Penial hooks of small size (<0.08 mm in length), slightly expanded and conical at base, tip sharp and directed towards genital orifice (Fig. 6B, E, F ).

Vagina (v) very short and stout, ~ 1/7 of penis length. Gametolytic duct (gd) a long and slender tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) convoluted and distally long and thick, ~ 3 times of vagina length. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing short and thickened seminal vesicle (sv) and ca. same length as from talon to branching point of seminal vesicle (Fig. 4C ).

Vaginal wall generally with thickened reticulated vaginal folds, smooth surface, and vaginal pores present (Fig. 6A, G ).

Radula . Each row consists of ~ 21-33 teeth with formula (16-10)-1-(10-16). Central tooth small with pointed cusp. Lateral and marginal teeth largest and undifferentiated, unicuspidal, and lanceolate. Latero-marginal teeth rapidly reducing in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 24B ).

Etymology.

The specific name paurodeviatus is derived from the Greek word pauros meaning little or few and the Latin word devius meaning out of the way. It refers to the last whorl of the new species as being slightly axially deflected and extruded from the penultimate whorl.

Distribution.

The species is only known from the type locality in southern Myanmar (Fig. 1 ).

Remarks.

Variation occurs in the possession of supracolumellar lamellae in some specimens. Currently, two species of Discartemon ( D. paurodeviatus sp. nov. and D. tonywhitteni ) have been recognized from Myanmar ( Sutcharit et al. 2020). These two species are noticeably different in shell morphology and internal structure of genitalia and found in distant localities from each other.

Figures

Figure 1. Approximate sampling locations used in this study. The location name and coordinates are listed in Table 1. Historical type localities of a broad scale, such as Tavoy, Burma, Moulmein, Mergui, and Tenasserim, are not indicated on this map.

Figure 2. Living snails A Discartemon tonywhitteni from near Phra (Buddha) Cave, Tanintharyi Region (shell width ~ 10 mm) B Discartemon paurodeviatus sp. nov. from the type locality (shell width ~ 11 mm) C Haploptychius heliakosus sp. nov. from the type locality (shell height ~ 9 mm) D Carinartemis exacutus from Lun Nga Mountain, Kayin State (shell height ~ 14 mm) E, F Carinartemis sankeyi (E) from Kayon Cave, Mon State (shell height ~ 10 mm) and (F) from Saddan Cave, Mawlamyine, Mon State (shell height ~ 10 mm).

Figure 3. A, B Discartemon tonywhitteni, specimen CUMZ 6264 from Phra (Buddha) Cave, Tanintharyi Region C-E Discartemon paurodeviatus sp. nov. C holotype CUMZ 13002 with apertural dentition and D, E paratypes CUMZ 13003 from the type locality.

Figure 4. Genital anatomy of A, B Discartemon tonywhitteni, specimen CUMZ 13001 A reproductive system and B insertion of vas deferens into penial sheath C, D Discartemon paurodeviatus sp. nov., paratype CUMZ 13003 C reproductive system and D insertion of vas deferens into penial sheath.

Figure 6. Internal sculpture of genitalia of Discartemon paurodeviatus sp. nov., paratype 13003 A junction of atrium, vagina, and proximal penis B, C lateral view of penial hooks on proximal part of penis D reticulated arrangement of penial hooks on middle part of penis E lateral view of penial hooks F arrangement of penial hooks on distal part of penis G arrangement of thickened reticulated vaginal folds.

Figure 24. Radula of specimens A Discartemon tonywhitteni, paratype CUMZ 13001 B Discartemon paurodeviatus sp. nov., paratype CUMZ 13003 C Haploptychius heliakosus sp. nov., paratype CUMZ 13014 D Carinartemis exacutus, specimen CUMZ 13021 E, F Carinartemis sankeyi, specimen CUMZ 13029 E overview of radula and F high magnification of central teeth.