Haploptychius pellucens (Pfeiffer, 1863)

Inkhavilay, Khamla, Siriboon, Thanit, Sutcharit, Chirasak, Rowson, Ben & Panha, Somsak, 2016, The first revision of the carnivorous land snail family Streptaxidae in Laos, with description of three new species (Pulmonata, Stylommatophora, Streptaxidae), ZooKeys 589, pp. 23-53 : 26-29

Taxon classification Animalia Pulmonata Streptaxidae

Haploptychius pellucens (Pfeiffer, 1863) Figs 1, 2A, 3 A–C, 7A, B, 8 A–D, 9 A–F, 10G; Table 1

Streptaxis pellucens Pfeiffer 1863 [1862]: 273, pl. 36, fig. 6. Type locality: Lao Mountain, Camboja [Cambodia]. Martens 1867: 85. Pfeiffer 1868: 441. Pfeiffer 1871: 29, pl. 115, figs 11, 12. Morlet 1883: 105, pl. 4, fig. 2, 2a. Tryon 1885: 71, 72, pl. 14, figs 98-100. Gude 1903: 212.

Haploptychius pellucens - Kobelt 1906: 132, 133, pl. 61, figs 17-20. Richardson 1988: 217, 218. Schileyko 2011: 24, 25.

Material examined.

This species was described from the H. Cuming collection. An illustration of the shell and one set of measurements were given in the original description. Three specimens from the Cuming collection at NHM have Pfeiffer’s handwritten label stating the species name and locality. In order to stabilise the name, an identical specimen matching with the illustration and measurements given in the original description is designated here as lectotype NHMUK 20160249.1 (Fig. 3A; H = 11.7, W = 11.2). The other two remaining shells from the same lot then became paralectotypes NHMUK 20160249.2 (2 shells; Fig. 3B; H = 11.1, W = 10.6 and H = 13.1, W = 13.4).

Cambodia: NHMUK MacAndrew coll. (4 shells). Ban Namone, Xayabouly, Laos (about 40 Km. from Ngeun District, Lao-Thai border to Xayabouly District): CUMZ 6264 (Fig. 3C; 8 shells), 6265 (4 specimens in ethanol). Tam Phatok, Ngoi, Luang Phrabang, Laos: CUMZ 6267 (7 shells). Ngoi, Luang Phrabang, Laos: CUMZ 6268 (7 shells). Nam Ork Roo, Nathong, Namor, Oudomxay, Laos: CUMZ 6269 (29 shells), 2670 (6 specimens in ethanol; Figs 3A, B, 8A, 9 A–F, 10G). Ban Oudom, Pak Beng, Oudomxay, Laos: CUMZ 6271 (15 shells). Tam Kao Rao, Vieng Phoukha, Luang Namtha, Laos: CUMZ 2672 (2 shells). Tam Mung Korn, Khamkeurt, Bolikhamxay, Laos: CUMZ 6266 (4 shells).

Description.

Shell. Shell oblique-ovate, white and translucent. Whorls 6½, spire conical with distinct suture. Shell surface glossy with thin transverse ridges which diminish below periphery. Embryonic shell about 2½ whorls, with smooth surface; following whorls regularly coiled. Penultimate whorl and last whorl rounded, axially deflected. Aperture subcircular; peristome thin, little expanded and reflected. Apertural dentition with one more or less strong parietal lamella. Umbilicus open and deep (Fig. 3 A–C).

Radula. Each row consists of 77-85 teeth with formula (38-42)-1-(38-42). Central tooth very small, triangular, with a pointed cusp. Lateral and marginal teeth undif ferentiated, lanceolate, unicuspid. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 10G).

Genital organs. Atrium (at) short. Proximal penis (p) stout about one-thirds of penis length; distal penis slender. Penial sheath (ps) thin, extending about half of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserted apically at penial sheath (Fig. 6A). Vas deferens (vd) passes through about one-third of penial sheath length before entering into penis apically. Penial retractor muscle (pr) very thick and connected at penis apically (Fig. 7A, B).

Internal wall of atrium generally corrugated with numerous atrial pores (Fig. 9A). Penial wall densely covered in light brown penial hooks, about 6 hooks/200 μm 2. Hooks located on low conical penial papillae, separated by thin reticulated folds. Penial hooks small (<0.1 mm in length), long, slender, slightly expanded at base, tips pointed and curved towards genital orifice (Fig. 9 B–E).

Vagina (v) short, about one-third of penis length. Gametolytic duct (gd) long tube extending to albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) proximally large with almost equal diameter to vagina, becoming narrower 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 and thin seminal vesicle. Seminal vesicle (sv) about three times longer than the length from talon to branching point of seminal vesicle (Fig. 7A).

Vaginal wall with series of transverse and undulated parallel vaginal folds; vaginal hooks absent (Fig. 9F).

Distribution.

This species is known from several limestone areas from central to northern part of Laos. The animals can be found at altitudes from 150-300 meters above mean sea level.

Remarks.

This species can be distinguished from Haploptychius porrectus by having a larger shell, more elevated spire elevated and less oblique aperture. The vas deferens passes through a shorter part of the penial sheath length, and the vagina wall has undulated transverse ridges rather than papillae. Haploptychius pellucens can be distinguished from Haploptychius costulatus ( Möllendorff, 1881) from China by having a larger and thinner shell, narrower umbilicus andhaving the left periphery of the penultimate whorl extending beyond the diameter of the last whorl. Haploptychius fischeri differs from this species by having a larger, more depressed and thicker shell, with a more obtuse spire, and subquadrangular aperture (Fig. 3G).

All live adult specimens were dissected and the genitalia have been examined, and three different types of genitalia are observed. There are six fully adult specimens collected from Nam Ork Roo, Oudomxay with ‘normal’ genitalia (Fig. 8A). Two specimens from Ban Namone, Xayabouly have no male genital organs (penis, retractor muscle, vas deferens and prostate gland), while female genital organs are well developed and fully function (Fig. 8D). This is apparently the first report of aphallic animals in Streptaxidae . The other two specimens from Ban Namone, have a ‘normal’ penis, but have an enlarged and curved "vaginal caecum (vc)" near the penis and atrium junction (Fig. 8B, C). This too is an unusual or unique structure in Streptaxidae . Nevertheless, all these animals appear conspecific based on their shells and the causes of this variation are unknown.