Trichelix horrida (Pfeiffer, 1863)

Sutcharit, Chirasak, Inkhavilay, Khamla & Panha, Somsak, 2020, Taxonomic note on Trichelix horrida (Pfeiffer, 1863) from Laos, with a type catalogue of Moellendorffia, Trichelix, and Moellendorffiella (Heterobranchia, Camaenidae), ZooKeys 952, pp. 65-93 : 65

Trichelix horrida (Pfeiffer, 1863) Figures 1 , 2 , 7B

Helix horrida Pfeiffer 1863 [ “1862”]: 272, pl. 36, fig. 15. Type locality: "Lao Mountains, Camboja" [probably in northern Laos around Luang Phrabang area, Laos]. Pfeiffer 1868a: 395. Pfeiffer 1868b: 399, 400, pl. 92, figs 17-19. Pfeiffer and Kobelt 1880: 579, pl. 170, figs 8-10.

Helix (Trihelix) horrida : Ancey 1887: 64. Pilsbry 1890: 9, pl. 1, figs 9-11.

Helix (Moellendorffia) horrida : Pilsbry 1895: 290.

Moellendorffia (Trichelix) horrida : Zilch 1960: 612. Inkhavilay et al. 2019: 105, figs 53f, 54a, 58h.

Moellendorffia horrida : Richardson 1985: 185.

Type material.

Three specimens originating from H. Cuming’s collection with the original label stating the taxon name and collection location in Pfeiffer’s handwriting are present in the malacological collection of the NHMUK. Of these specimens, the one most closely matching the measurements given in the original description is here designated as the lectotype NHMUK 20200202/1 (Fig. 7B ) to stabilize the name. The other two shells from the same lot become paralectotypes NHMUK 20200202/2 to 20200202/3.

Trichelix horrida was originally described based on specimens collected by H. Mouhot, with "Lao Mountain, Camboja" as the published type locality. Our survey following Mouhot’s itinerary in the south-western part of Cambodia yielded no specimens that could be identified in this genus. This record type locality seems to be imprecise. On the other hand, our survey in the northern part of Laos, where Mouhot had visited Luang Phrabang in 1861, recorded populations of this species in Muang Ngoi about 90 km north of Luang Phrabang City. Therefore, we restricted the known distribution and propose Luang Phrabang Province, Laos as the correct type locality for this species.

Material examined.

Moist evergreen forest on limestone hills between Ban Pha Toke and Ban Nong Ian, Muang Ngoi (Town), Ngoi District, Luang Phrabang Province, Laos (20°32'31.2"N, 102°38'56.3"E): CUMZ 5248 (eight specimens in ethanol; Fig. 1A ), CUMZ 5249 (five shells; Fig. 1B ), CUMZ 5250 (one shell).

Measurement.

From 10 specimens analyzed; shell height ranged from 12.4-14.7 mm (mean 13.5 ± 1.0); shell width ranged from 20.8-23.9 mm (mean 22.0 ± 1.2); and whorl count ranged from 6-6⅛ whorls.

Shell.

Shell medium-sized, dextral, slightly thin, translucent, depressed globose, biconcave shaped (dorsoventrally concave), and deeply umbilicate. Whorls 5-6, slightly convex, and increasing regularly; suture depressed, spire concave, looking like umbilicus. Embryonic shell large with very fine growth lines. Following whorl with corneous to brownish periostracum; upper surface with long hairs arranged in oblique rows; lower surface with slightly shorter hairs and few hairs around umbilicus. In worn specimens, shell surface possesses rough rows of tubercles running obliquely and descending, relatively smooth around umbilicus. Last whorl well rounded and little convex below periphery. Last whorl descending about ¼ whorl from aperture, and constriction occurs close to apertural lip. Aperture ear-shaped and opened subventrally; lip margin pale corneous, little thickened, and continuously expanded. External furrow aligns with internal apertural lamella or fold. Upper periphery marked with two furrows arranged spirally and correspond with palatal lamella and fold; below periphery with one furrow close to lip aligned with basal lamella. Parietal callus thickened, elevated, emarginated, and obtusely projecting inward. Umbilicus wide, but narrower than apex side which is cascade-shouldered.

Genitalia.

Atrium (at) short; penis (p) long; proximally with penial verge and enlarged fold at penial verge base; distally similar in length as proximally and somewhat slender tube. Epiphallus (e) slightly enlarged and almost the same length as penis. Flagellum (fl) very short and small. Vas deferens (vd) a small tube, follows vagina and penis, and connects distally on epiphallus and free oviduct. Penial retractor muscle (pr) slightly thickened and long (Fig. 2A ).

Internal wall of penis ribbed by a series of swollen longitudinal penial pilasters (pp). Smooth pilasters line introverts penial chamber and encircles penial verge tip. Penial verge (pv) small, short conic with smooth surface (Fig. 2B ).

Vagina (v) of similar length to proximal penis and held in position by series of muscles attached to foot floor. Gametolytic organ (duct and sac) long, cylindrical, and extending as far as albumen gland. Gametolytic duct (gd) as wide as gametolytic sac (gs) for most of its length but narrows before reaching gametolytic sac. Free oviduct (fo) short, about half of vagina length; oviduct (ov) small. Prostate gland (pg) and oviduct (ov) developed; hermaphroditic duct long and convoluted tube; albumen gland solid and tongue shape (Fig. 2A ).

Internal wall of vagina possesses several longitudinal vaginal pilasters (vp). Pilasters with smooth surface and line entire vaginal chamber (Fig. 2B ).

Animal.

Live animal covered with blackish-brown reticulated skin and dorsally with whitish stripe in middle of the body. A small curved head wart (hw) is located between the posterior tentacles (Fig. 2C ). Foot narrow and long; mantle edge greyish; tentacles brownish, and lower tentacles pale brown. Mantle cavity possesses blackish pigmentation. Live snails possess short to long periostracal hairs, which mostly disappear in worn shells or old snails.

Radula.

Teeth arranged in anteriorly pointed, V-shaped rows; each row contains about 75 (37-(18-20)-1-(18-20)-38) teeth. Central tooth unicuspid, triangular with blunt cusp. Lateral teeth unicuspid, triangular with blunt tip, gradually taller laterally and little inclined to central tooth. Marginal teeth starting around tooth numbers 18 to 20 outwards from lateral teeth. Tricuspid or bicuspid marginal teeth, endocone usually absent; mesocone large, broad and with curved to blunt cusp; ectocone slightly large, pointed head and located at base of the teeth. Outer marginal teeth rather small; mesocone and ectocone indistinguishable, with undulated cusp (Fig. 2D ).

Distribution.

Trichelix horrida was previously known only from the type locality ("Lao Mountain, Cambojia" [Cambodia or Laos]). The specimens examined herein were collected from limestone karst in Muang Ngoi Town, about 90 km north of Luang Phrabang City.

Our sampling locality was characterized by monsoonal karst landforms with high humidity. The snails occurred in tropical moist deciduous forest. There was heavy rain before our visit in August 2014. The snails were active, crawling or sitting on moist rotten logs among the limestone outcrops.

Remarks.

Trichelix horrida is distinctly different in shell morphology from all other Moellendorffia species by having a concave spire, rounded last whorl, and two furrows arranged spirally on the upper periphery (Table 1 ). In contrast, Moellendorffia species tend to have flattened to elevated spires, rounded to shouldered last whorls, and two furrows arranged vertically on the periphery. Trichelix horrida differs from the other congeners in having two short furrows on the last whorl and an elevated parietal callus (Fig. 7B ), while T. biscalpta and T. hiraseana tend to have a long furrow on the last whorl and unelevated parietal callus (Figs 6C , 7A ). In addition, T. hiraseana has a relatively long, drumstick-shaped flagellum, while the type species has a very short protrusion (see Minato 2011 for a comparison). In addition, Chloritis bifoveata (Benson, 1850) from Myanmar and Thailand, C. diplochone Möllendorff, 1898 from Laos and Thailand, and C. vinhensis Thach & Huber, 2018 from Vietnam differ from T. horrida by having a thin parietal callus, with a shell constriction occurring about half a whorl from the aperture (absent in C. vinhensis ), and without apertural dentition ( Sutcharit and Panha 2010; Páll-Gergely and Neubert 2019; Páll-Gergely et al. 2020).

Figures

Figure 1. Living snail and shell A specimen CUMZ 5248 B specimen CUMZ 5249.

Figure 2. Genitalia and radula of T. horrida specimen CUMZ 5248 A General view of the genital system B Interior structure of the penis and vaginal chambers C Dorsal view showing head wart D Scanning electron micrographs of central, lateral and marginal teeth. Central tooth is indicated by ' C' and the other numbers indicate the order of lateral and marginal teeth.

Figure 6. A Moellendorffia spurca, syntype MNHN-IM- 2000 - 1992 B Moellendorffia trisinuata, syntype ZMB 7620 C Trichelix biscalpta, syntype MCZ 167125 D Trichelix diminuta, lectotype ANSP 90049 E Trichelix eucharista, lectotype ANSP 81221 F Trichelix hiraseana, lectotype SMF 7404 / 1 of Stegodera helleri. Photo: AJ Baldinger (C).

Figure 7. A Trichelix hiraseana, lectotype ANSP 89999 B Trichelix horrida, lectotype NHMUK 20200202 / 1 C Trichelix eucharista, syntype NHMUK 19991540 of Chloritis malangensis D Trichelix oshimana, syntype NHMUK 1922.8.29.83 E, F Trichelix tokunoensis E lectotype ANSP 87680 and F paralectotype ANSP 90048.