Hemiplecta humphreysiana (Lea, 1840)

Sutcharit, Chirasak & Panha, Somsak, 2021, Systematic review of the dextral Hemiplecta Albers, 1850 (Eupulmonata, Ariophantidae) from Thailand with description of a new species and list of all the Indochinese species, ZooKeys 1047, pp. 101-154 : 101

Hemiplecta humphreysiana (Lea, 1840)

Figures 1A , 2A, B , 3 , 10A-C

Helix humphreysiana Lea, 1840: 175. Type locality: Pondicherry and Singapore. Lea 1841: 463, 464, pl. 12, fig. 16. Reeve 1854: Helix pl. 74, species 387.

Hemiplecta humphreysiana : Morgan, 1885a: 378. Godwin-Austen 1898: 74, pl. 80. figs 6, 6b; pl. 61, figs 1, 1e. Collinge 1902: 78, pl. 4, figs 16-23. Laidlaw 1932a: 78. Laidlaw 1932b: 40. Laidlaw 1933: 217. Benthem Jutting 1949: 69. Benthem Jutting 1950: 444, fig. 64. Laidlaw 1957: 134. Benthem Jutting 1959: 148-150. Ho 1995: 104, 105.

Nanina humphreysiana : Martens, 1867: 233, pl. 10, figs 2, 2b, 4. Tryon, 1886: 36, pl. 11, figs 52, 53, pl. 12, fig. 54.

Nanina (Hemiplecta) humphreysiana : Tryon, 1886: 36, pl. 11, figs 52, 53; pl. 12, fig. 54.

Type specimen.

See the species list of the Indochinese species (Fig. 12D ).

Material examined.

Singapore: Bukit Timah : RMBR 1990.1711 (1 specimen in ethanol), 1990.15781-2 (2 specimens in ethanol); CUMZ 4573 (1 shell; Figs 2A , 3 ). Botanic Garden: RMBR 1975.2.10.89 (1 shell), RMBR 1990.1710 (1 specimen in ethanol); CUMZ 4571/1 (1 shell), CUMZ 4572 (4 specimens in ethanol). Nee Soon: RMBR 1990.15945 (1 shell), RMBR 1990.16996 (1 specimen in ethanol), RMBR 1990.15103-4 (2 specimens in ethanol), RMBR 1992.3159 (1 specimen in ethanol), RMBR 1992.3160-1 (2 shells), RMBR 1992.3162 (1 specimen in ethanol), RMBR 1994.4116 (1 specimen in ethanol). Singapore: RMBR 1989.509-513 (5 shells), RMBR 1990.15105 (1 specimen in ethanol) . Thailand: Sirindhorn Waterfall, Halabala National Park , Narathivat Province: CUMZ 4647 (2 shells), CUMZ 4648 (1 shell; Fig. 2B ) .

Shell. Shell large (height up to 40 mm, width up to 55 mm), dextral and conic to depressed conic (Fig. 2A, B ). Whorls 6 to 8, slightly convex; suture wide and shallow. Shell yellowish to brownish, usually with narrow dark brown band on periphery. Upper shell surface darker than lower surface. Apex obtuse; embryonic shell large and smooth; following whorls with thin growth lines. Last whorl rounded to slightly angulate; aperture ovate; lip simple but slightly thickened in adult snail. Columella slightly dilated; parietal callus thin and translucent. Umbilicus open and deep.

Genitalia. Atrium (at) very short (Fig. 3A ). Penis (p) long, slender, cylindrical, and encircled by thin penial sheath (psh) extending about one-third of penis length. Epiphallic caecum (ec) short, straight; penial retractor muscle (pr) thin and attached to the tip. Epiphallus (e) short and about one-third of penis length. Flagellum (fl) short, stout, and with thin muscle bands connected to penial sheath. Vas deferens (vd) small tube. Internal wall of penis with sculpture encircling penial verge (Fig. 3B ). Penial sculpture (ps) consists of scattering of small papillary knobs arranged randomly on penial wall. Penial verge (pv) long conic with smooth surface.

Vagina (v) long and cylindrical (Fig. 3A, B ); internal wall with thin and smooth longitudinal vaginal pilasters (vp). Dart apparatus (da) long muscular cylinder, externally and internally smooth; dart papilla (dp) short, conic, and smooth. Gametolytic sac (gs) elongate or bulbous without distinct duct. Free oviduct (fo) long and encircled with thickened blackish muscular tissue (orange in fresh specimens). Oviduct (ov) long and with lobules; prostate gland bound to oviduct. Albumen gland (ag) small. Hermaphroditic duct (hd) small, convoluted, and connected to lobules of hermaphroditic gland (hg).

Radula. Each row containing about 253 teeth (127-(18-32)-1-(29-32)-125). Central tooth unicuspid and triangular (Fig. 10A ). Lateral teeth unicuspid, slanted, and with curved cusp. Outer lateral teeth with slightly curved cusps; latero-marginal transition from tooth numbers 28 to 32 (Fig. 10B ). Marginal teeth bicuspid and curved; endocone and ectocone usually similar in shape and size (Fig. 10C ).

External features. Mantle edge with large dorsal lobes. Right dorsal lobe (rdl) to right of anus (an; on the left in figure), large, and thick. Left dorsal lobe to left of anus (on the right in figure), composed of thin crescentic anterior left dorsal lobe (aldl), and thin elongated posterior left dorsal lobe (pldl). Right shell lobe (rsl) and left shell lobe (lsl) have short finger-shaped extensions located on mantle edge near tip of urinary groove and around junction of anterior and posterior left dorsal lobes, respectively, (Fig. 3C, D ).

Pulmonary cavity typically sigmurethran, heart (h; auricle and ventricle) located left of kidney (k; on the right in figure). Pulmonary cavity approximately four times longer than wide. Pulmonary vein (puv) and venation on lung cavity well developed and distinct. Kidney (k) elongate, slender, and approximately one-third length of pulmonary cavity. Ureter (ur) sigmoid, closed tube arising from tip of kidney, extending along right side of kidney, and curved adjacent to rectum (r). Anus (an) adjacent to mantle edge (Fig. 3C ).

Living snails possess long greyish-brown tentacles (Fig. 1A ). Skin reticulated brownish with blackish reticulations around head. Foot sole relatively elongate, broad and unipartite. Sole of foot plain brownish; side of body brownish; upper part of tail dark greyish. Tail long, curved mid-dorsally, tall dome-shaped in cross section. Caudal horn not overhanging; caudal foss a long vertical slit arranged on tail above sole margin. Pedal groove typical aulacopod and well defined (Fig. 3E ).

Distribution.

The systematic studies of some Hemiplecta species have revealed incongruence between the traditional shell-based and molecular classifications ( Sutcharit et al. 2021). Therefore, apart from Singapore (type locality) the historical record of H. humphreysiana from Sumatra, Borneo, and several localities in Peninsular Malaysia ( Martens 1867; Tryon 1886; Godwin-Austen 1898; Collinge 1902; Laidlaw 1932a, 1933, 1957; Benthem Jutting 1950, 1959) needs to be confirmed by more convincing morphological and molecular evidences. In Thailand, this is the first and only record of this species from Narathivat, the southern-most province of Thailand.

Remarks.

The specimens examined and described herein for the genitalia, pallial system, and radula were collected from Singapore (the correct type locality of this type species) to specify the characteristics for the genus. Hemiplecta humphreysiana clearly differs from all other species recorded both in Thailand and Peninsular Malaysia (compared with the type specimens in the list of the species). It can be distinguished from H. floweri Smith, 1899 (see Godwin-Austen 1900) from Peninsular Malaysia, by having a narrow umbilicus, without a brownish spiral band on the umbilical area, and more elevated spire (Smith 1898; Godwin-Austen 1900). In addition, the straight epiphallic caecum of this species is distinct from the coiled epiphallic caecum of H. floweri (Table 2 ). Unfortunately, none of the penial sculptures have been prepared for further comparison.

Figures

Figure 1. Living snail. A Hemiplecta humphreysiana from Singapore (width about 45 mm) B, C Hemiplecta distincta B from Saraburi, Thailand (width about 65 mm) and C mating pairs D, E Hemiplecta funerea from Nan, Thailand (width about 50 mm) D yellow shell form and E dark shell form (width about 50 mm) F Hemiplecta esculenta from Chiang Mai, Thailand (width about 30 mm).

Figure 2. A, B Hemiplecta humphreysiana A specimen CUMZ 4573 from Singapore and B specimen CUMZ 4648 from Narathivat, Thailand C Hemiplecta distincta, specimen CUMZ 4531 from Chacheongsao, Thailand.

Figure 3. Genitalia, pallial system, mantle edge structure, and caudal region of Hemiplecta humphreysiana, specimen CUMZ 4573 from Singapore A whole genital organs B internal wall sculpture of penis, vagina and dart chamber C pallial system, lung cavity and ventral view of mantle edge D dorsal view of mantle edge showing shell lobes and E right view of caudal region.

Figure 10. Representative SEM images of radula A-C Hemiplecta humphreysiana, specimen CUMZ 4573 from Singapore A central and lateral teeth B transition from lateral teeth to marginal teeth and C outermost marginal teeth D, E Hemiplecta distincta, specimen CUMZ 4560 from Chanthaburi, Thailand D central and lateral teeth and E outermost marginal teeth F, G Hemiplecta funerea, specimen CUMZ 4575 from Nan, Thailand F central and lateral teeth and G outermost marginal teeth H, I Hemiplecta esculenta, specimen CUMZ 4553 from Chiang Mai, Thailand H central and lateral teeth I transition from lateral teeth to marginal teeth J Hemiplecta nemorosa sp. nov., paratype CUMZ 5253 from Maehongsorn, Thailand. Central tooth indicated by ' C'. Numbers indicate the tooth order from lateral to marginal end.

Figure 12. A Hemiplecta denserugata, syntype SMF 226943 / 1 B Hemiplecta distincta, holotype MNHN-IM- 2000 - 35535 of Hemiplecta franzhuberi Thach, 2020 C Hemiplecta funerea, lectotype NHMUK 1896.1.25.4 D Hemiplecta gordoniae, specimen NHMUK 1903.7.1.309 E Hemiplecta humphreysiana, syntype NMNH 116569.