Hemiplecta distincta (Pfeiffer, 1850)

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 distincta (Pfeiffer, 1850)

Figures 1B, C , 2C , 4 , 10D, E

Helix distincta Pfeiffer, 1850: 69, 70. Type locality: Insulis Moluccis [possibly error or mislabeling]. Pfeiffer 1853: 346, pl. 134, figs 1, 2. Reeve 1854: Helix pl. 86, species 465.

Nanina distincta : Martens, 1860: 7.

Helix neptunus Pfeiffer, 1861a: 190. Type locality: Siam [Thailand]. Pfeiffer 1861b: 176, 177. pl. 48, figs 1, 2. New synonym

Nanina (Rhyssota) distincta : Martens, 1867: 69, 70, pl. 6, fig. 8.

Nanina (Hemiplecta) distincta : Tryon, 1886: 30, pl. 8, fig. 26.

Nanina (Hemiplecta) neptunus : Tryon, 1886: 34, pl. 8, fig. 27.

Hemiplecta zimmayensis Godwin-Austen, 1888c: 241, 242. Type locality: Zimme, Siam territory [Chiang Mai Province, Thailand]. New synonym

Ariophanta (Hemiplecta) distincta : Morelet, 1891: 231.

Hemiplecta distincta : Morelet, 1889: 124. Blanford 1903: 277, 278. Panha 1987a: 108-115, figs 1-3. Panha 1987b: 25-34, fig. 9. Panha 1988a: 197-206, figs 6, 7. Panha 1988b 233-239. Panha 1994: 4-15. Inkhavilay et al. 2019: 76, figs 35b, c, 56c.

Nanina (Rhysota) distincta : Fischer and Dautzenberg 1904: 393. Dautzenberg and Fischer 1906: 346, 347.

Nanina (Rhysota) distincta var. neptunus : Dautzenberg and Fischer 1908: 171.

Koratia distincta : Godwin-Austen 1919: 199-202, figs 1, 2. Schileyko 2002: 1282, 1283, fig. 1685.

Nanina (Rhysota) distincta neptunus : Dautzenberg and Fischer, 1906: 347, 348.

Hemiplecta (Koratia) distincta : Solem, 1966: 27.

Hemiplecta (Hemiplecta) distincta : Hemmen and Hemmen, 2001: 44, fig. 12.

Hemiplecta (Hemiplecta) neptunus : Hemmen and Hemmen, 2001: 44.

Hemiplecta (Hemiplecta) zimmayensis : Hemmen and Hemmen, 2001: 44.

Type specimen.

See the species list of Indochinese species (Fig. 11C ).

Material examined.

Thailand: Tam Chiang Dao, Chiang Mai: CUMZ 4550 (1 shell), CUMZ 4558 (5 shells). Wang Chao Waterfall, Kampangphet: CUMZ 4641 (4 shells). Klong Lann National Park, Kampangphet: CUMZ 4579 (2 specimens in ethanol). Kaeng Jed Kwae, Watbot, Phitsanuloke: CUMZ 4638 (7 shells). Tam Wang Daeng, Nern Maprang, Phitsanuloke: CUMZ 4632 (1 shell). Khao Nang Rum, Huay Kla Klang National Park, Uthaithani: CUMZ 4502 (6 shells), CUMZ 4510 (3 shells), CUMZ 4538 (3 shells), CUMZ 4541 (6 shells), CUMZ 4607 (6 shells), CUMZ 4610 (9 shells), CUMZ 4611 (3 shells). Jed Sow Noi Waterfall, Muaklek, Saraburi: CUMZ 4548 (3 shells). Pu Kare Botanic Garden, Saraburi: CUMZ 4505 (4 shells), CUMZ 4506 (1 shell), CUMZ 4534 (5 shells). Tam Dao Khao Kaew, Muaklek, Saraburi: CUMZ 4624 (1 shell). Wat Tharahat, Saraburi: CUMZ 4508 (1 shell), 4530 (1 shell). Sam Larn National Park , Saraburi: CUMZ 4578 (2 specimens in ethanol). Bang Srithong, Bang Kruay, Nonthaburi: CUMZ 4555 (5 shells). Khao Look Chang, Pakchong, Nakhonratchasima: CUMZ 4501 (8 shells), CUMZ 4606 (9 shells), CUMZ 4612 (9 shells), CUMZ 4535 (3 shells). Tub Lann National Park , Nakhonratchasima: CUMZ 4617 (1 shell). Nawang, Nongbualumphu: CUMZ 4529 (1 shell). Tam Suwankuha, Nongbualumphu: CUMZ 4633 (3 shells), 4637 (3 shells). Thung Kra-Mang, Phu Kiew Wildlife Sanctuary, Chaiyaphum: CUMZ 4608 (5 shells). Pang Khone, Sakonnakhon: CUMZ 4619 (4 shells). Phuphan Mountains , Sakonnakhon: CUMZ 4504 (6 shells), CUMZ 4507 (5 shells). Phu Kum Khao, Sahatsakhan, Kalasin: CUMZ 4557 (8 shells). Phu Sri Tharn Wildlife Sanctuary, Kalasin: CUMZ 4621 (1 shell). Huay Lao Waterfall, Phuluang Wildlife Sanctuary, Loei: CUMZ 4634 (1 shell). Tam Pha Bend, Chiang Karn, Loei: CUMZ 4532 (1 shell). Tam Pha Bing, Wangsapung, Loei: CUMZ 4636 (1 shell). Tam Piya, Loei: CUMZ 4639 (3 shells). Tam Mahasombat, Lomsak, Phetchabun: CUMZ 4567 (1 shell). Tam Yai Namnao, Namnao National Park , Phetchabun: CUMZ 4566 (1 shell), CUMZ 4622 (1 shell). Tam Phraya Nakarat, Phuphaman National Park , Khonkaen: CUMZ 4635 (1 shell). Pha Tam National Park , Ubonratchathani: CUMZ 4604 (3 shells), CUMZ 4616 (3 shells). Yod Dome National Park , Buriram: CUMZ 4629 (2 shells). Wang Ta Krai Waterfall, Nakhonnayok: CUMZ 4540 (2 shells), CUMZ 4549 (2 shells), CUMZ 4605 (1 shell), CUMZ 4640 (5 shells), CUMZ 4577 (1 specimen in ethanol). Khao Ang Rue Nai Wildlife Sanctuary, Chachoengsao: CUMZ 4531 (1 shell; Fig. 2B ), CUMZ 4546 (7 shells), CUMZ 4609 (3 shells), CUMZ 4613 (4 shells), CUMZ 4620 (2 shells), CUMZ 4627 (1 shell), CUMZ 4630 (1 shell). Pang Srida National Park , Prachinburi: CUMZ 4631 (4 shells). Ra-Ru, Taphraya, Srakeow: CUMZ 4628 (1 shell). Tam Leum, Klonghad, Srakeow: CUMZ 4625 (1 shell). Khao Cha Ang-Oan, Borthong, Chonburi: CUMZ 4542 (4 shells), CUMZ 4618 (1 shell), CUMZ 4626 (4 shells). Khao Cha Mao Waterfall, Rayong: CUMZ 4543 (1 shell). Tam Suwanphupha, Khao Chamao, Rayong: CUMZ 4545 (1 shell). Wat Ma-deau (Tam Khao Loi), Khao Chamao, Rayong: CUMZ 4544 (4 shells). Plieu National Park , Chanthaburi: CUMZ 4509 (1 shell), CUMZ 4536 (1 shell), CUMZ 4539 (9 shells), CUMZ 4560 (1 specimen in ethanol; Fig. 4 ), CUMZ 4601 (1 shell), CUMZ 4615 (4 shells). Sibha Shan Waterfall , Chanthaburi: CUMZ 4547 (6 shells). Tha Mai District , Chanthaburi: CUMZ 4603 (1 shell). Koh Kud , Trat: CUMZ 4559 (9 shells), CUMZ 4614 (7 shells). Kaeng Kracharn National Park , Phetchaburi: CUMZ 4527 (1 shell). Tam Nam Pud , Pangnga : CUMZ 4623 (1 shell) .

Shell. Shell large (height up to 55 mm, width up to 75 mm), yellowish with white narrow peripheral band, and paler color below on lower shell surface. Upper shell surface with thin growth lines interrupted with spiral wrinkles. Last whorl large and rounded; aperture large ovate; lip simple but slightly thickened in adult snails (Fig. 2C ).

Genitalia. The external genital organs were described in Godwin-Austen (1900, 1919). Gametolytic sac (gs) bulbous with undifferentiated duct. Internal wall of penis exhibits closely packed papilla knobs that abruptly cease near atrium; penial verge absent. Internal sculpture of vagina with thin and smooth longitudinal vaginal pilasters (vp). Internal surface of dart apparatus smooth; dart papilla (dp) conic, and with a smooth surface (Fig. 4A, B ).

Radula. Each row with about 543 teeth (276-(15-20)-1-(15-20)-276). Central tooth unicuspid triangular with rounded head (Fig. 10D ). Lateral teeth unicuspid, oblique and triangular. Outer lateral teeth unicuspid, sickle-shaped, with transition to curved and narrow sickle form; latero-marginal transition starts from tooth numbers 15 to 20. Marginal teeth narrowly curved, bicuspid; endocone and ectocone small and pointed (Fig. 10E ).

External features. Living snails have a similar soft body morphology and pulmonary cavity to that of H. humphreysiana . The distinct characters are pale brown to brownish body (Fig. 1B, C ). Sole of foot brownish; caudal horn not overhanging; caudal foss a long vertical slit arranged on tail above sole margin. Pedal groove typical aulacopod and well defined (Fig. 4E ). Mantle edge narrow with large dorsal lobes. Right dorsal lobe (rdl) to right of pneumostome, large and thick; left dorsal lobe to left of pneumostome, composed of anterior left dorsal lobe (aldl) and posterior left dorsal lobe (pldl); shell lobe absent (Fig. 4C, D ).

Distribution.

Ranges from Cambodia to Laos, Thailand and southern Vietnam ( Smith 1896; Laidlaw 1932a; Panha 1988a, 1994; Schileyko 2011; Inkhavilay et al. 2019). In Thailand, H. distincta is fairly abundant and occurs throughout the country, except for southern Thailand ( Panha 1988b, 1994). The southern limit of the species appears to be near the Isthmus of Kra (10°N). We have a single and old shell from Pangnga Province, southern Thailand that needs to be confirmed.

Remarks.

The type specimens of Helix neptunus Pfeiffer, 1861 and Hemiplecta zimmayensis Godwin-Austen, 1888 exhibit a shell morphology and color patterns identical to that of H. distincta . The absence of a whitish peripheral band in Helix neptunus Pfeiffer, 1861 and the strong growth lines of Hemiplecta zimmayensis are the only observed differences from H. distincta . Therefore, we recognize these two nominal species as junior subjective synonyms of H. distincta .

Hemiplecta distincta has long been considered a food item for local people in northeastern Thailand ( Panha 1987b), as well as in Cambodia and Laos (personal observation). It has also been found to be an intermediate host of the rat lungworm, a human pathogen ( Panha 1987b, 1988b). The life cycle and breeding biology of this species have been extensively studied ( Panha 1987a, b, 1988a, b, 1994).

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 4. Genitalia, mantle edge structure, and caudal region of Hemiplecta distincta, specimen CUMZ 4560 from Chanthaburi, Thailand A whole genital organ B internal wall sculpture of penis, vagina, and dart chamber C dorsal view of mantle edge D ventral view of mantle edge 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 11. A Hemiplecta auriettae, specimen NHMUK 1912.4.16.497 B Hemiplecta cymatium, specimen UMZC I. 104350 ex. Benson collection C Hemiplecta distincta, possible syntype NHMUK 20200199 D Hemiplecta floweri, syntype NHMUK 1899.3.16.1 - 2.