Haploptychius heliakosus 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

Haploptychius heliakosus Man & Panha sp. nov.

Figs 2C , 13D , 14A, B , 15 , 16 , 24C

Type material.

Holotype CUMZ 13013 (Fig. 13D ). Measurements: shell height 9.0 mm, shell width 10.2 mm, and 7 whorls. Paratypes CUMZ 13014 (24 shells; Fig. 14A ), CUMZ 13015 (15 specimens in ethanol), NHMUK (2 shells).

Type locality.

Bardai Mountain, Hpa-an Township, Hpa-an District, Kayin State, Myanmar (16°59'50"N, 97°41'48"E).

Other material examined.

Kyonknow Cave , Hpa-an Township, Hpa-an District, Kayin State, Myanmar (17°01'00.1"N, 97°41'42.1"E): CUMZ 13016 (7 shells; Fig. 14B ) .

Diagnosis.

Haplotychius heliakosus sp. nov. differs from H. bombax by having a deeper suture, higher spire, rounded penultimate whorl, and subquadrangular aperture. In contrast, H. bombax possesses a relatively shallower suture, lower spire, angular penultimate whorl, and semi-ovate aperture. Haplotychius heliakosus sp. nov. also differs from H. burmanicus and H. blanfordi by having an oblique ovate shell, higher spire, and less axially deflected last whorl. In contrast, the two latter species exhibit a depressed heliciform shell and lower spire, and more axially deflected last whorl. Although H. heliakosus sp. nov. has a shell similar to H. pellucens from Laos, this new species has a less axially reflected last whorl, subquadrangular aperture, and more ridges on the shell surface. Additionally, the genitalia of H. heliakosus sp. nov. has a thickened penial sheath covering almost the entire penis, and short and stout penial hooks on papillae, while H. pellucens has a thin penial sheath covering ~ 1/2 of the penis, and long and slender penial hooks without papillae. This new species differs from C. exacutus (Gould, 1856) by having penial sheath retractor muscle originating at atrium, vas deferens passing through a short section of thin penial sheath before extending ~ 1/3 of the penial sheath length to the curved portion, shorter free oviduct, seminal vesicle ca. twice the length from talon to branching point of seminal vesicle, thickened atrial folds with sparse atrial pores, and stout distal penial hooks.

Description.

Shell oblique-ovate, white, and translucent; whorls 7- 7½; spire low conical with distinct suture. Shell surface glossy with transverse ridge, nearly smooth with few transverse ridges near peristome. Embryonic shell large, ~ 2½ whorls with smooth surface; following whorls regularly coiled. Penultimate whorl rounded; last whorl axially deflected. Aperture subquadrangular; peristome discontinuous, thickened, expanded, and slightly reflected. Apertural dentition with one strong parietal lamella and sometimes with small second parietal lamella adjoined at a right angle. Umbilicus open and deep (Fig. 13D , 14A, B ).

Genital organs. Atrium (at) short. Penis (p) very thin, and long tube. Penial sheath (ps) muscularly enlarged, very thickened, and extending entire penis length; penial sheath retractor muscle (psr) thin, originating at atrium, and inserting distally on penial sheath (Fig. 15A ). Vas deferens (vd) passes through a short section of thin penial sheath then extends ~ 1/3 of the penial sheath length to a curved portion before entering penis distally. Curved portion with very thin connective tissue attached between vas deferens and penial sheath wall (Fig. 15B ). Penial retractor muscle (pr) thin, very long, inserting at junction of penis and vas deferens.

Internal wall of atrium generally smooth with transverse thickened atrial folds with sparse atrial pores (Fig. 16A ). Proximal penial wall with scattered pale brownish penial hooks, ~ 26 hooks/200 μm 2; hooks located on irregular trapezoidal penial papillae and separated by longitudinal folds (Fig. 16B ). Penial hooks small (<0.04 mm in length), slightly expanded at base, tips pointed, and slightly curving away from genital orifice (Fig. 16C ). Penial wall on middle to distal parts with scattered light brownish penial hooks, ~ 24 hooks/200 μm 2; hooks located on laterally-flattened penial papillae separated by longitudinal folds (Fig. 16D, E ). Penial hooks short, stout, small (<0.01 mm in length), expanded at base, tips obtuse and curved towards genital orifice (Fig. 16F-H ).

Internal wall of atrium generally smooth with sparse atrial pores (Fig. 23A ). Proximal penial wall covered with scattered and pale brownish penial hooks, ~ 12 hooks/200 μm 2. Proximal penial hooks located on laterally flattened penial papillae; hooks small and short (<0.03 mm in length), slightly expanded at base, tips obtuse and curved towards genital orifice (Fig. 23B, C ). Middle and distal penial walls densely covered with pale brownish hooks, ~ 20 hooks/200 μm 2. Middle and distal hooks located on laterally compressed penial papillae separated by reticulated folds; hooks small, short (<0.01 mm in length), slightly expanded at base, tips pointed (Fig. 23D-G ).

Vagina very short, stout, and ~ 1/10 of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) enlarged, tapering to a smaller tube in the middle part, then enlarged distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short, and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) of about twice the length from talon to branching point of seminal vesicle (Fig. 15A ).

Vaginal wall with longitudinal vaginal folds (Fig. 16I ), folds with nearly smooth surface, and vaginal hook absent.

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

Etymology.

The specific name heliakosus is derived from the Greek word heliakos meaning of the sun. It honors our colleague, Dr. Arthit Pholyotha, who collected the specimens and took the photos of the living snails used in this study. His first name Arthit means the Sun.

Distribution.

This new species is currently known from two localities in the limestone karsts near Salween (Thanlwin) Basin, Kayin State, southeastern Myanmar.

Remarks.

Shell variations of H. heliakosus sp. nov. were found between two populations. Specimens from the Kyonknow population (Fig. 14B ) have a straighter periphery or nearly cylindrical last whorl compared to those from the type locality, Bardai Mountain (Fig. 13D , 14A ). As no living specimens from the Kyonknow Cave were collected, we considered the Kyonknow population as an intraspecific variation of H. heliakosus sp. nov. because this locality is very close to the type locality. Living specimens from the Kyonknow population and genital examination are necessary to resolve these systematic issues.

Figures

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 13. A-C Haploptychius tenasserimicus sp. nov. A holotype CUMZ 13011 with apertural dentition B, C paratypes CUMZ 13012 from the type locality D Haploptychius heliakosus sp. nov. holotype CUMZ 13013 with apertural dentition.

Figure 14. A, B Haploptychius heliakosus sp. nov. A paratype CUMZ 13014 from the type locality and B specimen CUMZ 13016 from Kyonknow Cave, Hpa-an, Kayin State C-E Haploptychius karenorum sp. nov. C holotype CUMZ 13017 with apertural dentition D paratype CUMZ 13018 from the type locality and E specimen CUMZ 13019 from Taung Lay Cave, Hpa-an, Kayin State.

Figure 15. Genital anatomy of Haploptychius heliakosus sp. nov. paratype CUMZ 13014 A reproductive system B insertion of vas deferens into penial sheath.

Figure 16. Internal sculpture of genitalia of Haploptychius heliakosus sp. nov. paratype CUMZ 13014 A atrium surface B arrangement of penial hooks on proximal part of penis C top view of penial hook D, E arrangement of penial hooks on middle part of penis F top view of penial hook with obtuse tip G arrangement of penial hooks on distal part of penis H high magnification of penial hook with obtuse tip I vaginal folds.

Figure 23. Internal sculpture of genitalia of Carinartemis sankeyi, specimen CUMZ 13029 A atrium surface B arrangement of penial hooks on proximal part of penis C lateral view of exposed proximal penial hooks D penial hooks on middle part of penis E arrangement of penial hooks on distal part of penis F uncovered distal penial hooks with pointed tip G distal penial hooks embedded in penial papillae H vaginal surface with vaginal pores.

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.