Rhiostoma tigrina Tongkerd & Tumpeesuwan, 2023

Tongkerd, Piyoros, Tumpeesuwan, Sakboworn, Inkhavilay, Khamla, Prasankok, Pongpun, Jeratthitikul, Ekgachai, Panha, Somsak & Sutcharit, Chirasak, 2023, Systematic revision of the snorkel snail genus Rhiostoma Benson, 1860 (Gastropoda, Caenogastropoda, Cyclophoridae) with descriptions of new species, ZooKeys 1142, pp. 1-144 : 1

13. Rhiostoma tigrina Tongkerd & Tumpeesuwan sp. nov.

Figs 18 , 31 , 32F

Rhiostoma sp. 1- Tumpeesuwan 2001: 59-64, figs 4.19-4.21 (in part).

Type material.

Holotype CUMZ 4497/1 (cW 19.5 mm, cH 10.5 mm, dL 20.8 mm; Fig. 31A ). Paratypes CUMZ 3909 (29 adults + 10 juveniles), CUMZ 4497/2 (2 shells; Figs 31B , 32F ), CUMZ 4806 (13 adults + 5 juveniles; Fig. 31C ), CUMZ 10191 (6 adults + 4 juveniles), NHMUK 20220441 (5 shells), and SMF 368676 (5 shells). All paratypes are from the type locality.

Type locality.

Tham Pum Tham Pla, Mae Sai District, Chiang Rai Province, Thailand (20°21'00.4"N, 99°51'25.2"E). Limestone hill covered by dry deciduous forest.

Other material examined.

Thailand: Chiang Dao, North Thailand: ZMUC ex. B. Degerbøl collection (1 alcohol specimen at 400 m, and 2 alcohol specimens at 1100 m). Tham Samta, Muang , Maehongsorn : CUMZ 4441. Wat Pa Tham Wua , Pang Mapha , Maehongsorn : CUMZ 10028. Tham Luang , Khun Nam Nang Non , Mae Sai , Chiang Rai: CUMZ 10186, 10188. Tham Pha Chom , Mae Sai , Chiang Rai: CUMZ 4347. Tham Pla , Mae Sai , Chiang Rai: CUMZ 4346, 4803. Tham Saohin Prayanak , Mae Sai , Chiang Rai: CUMZ 3906, 4442, 10190, 10193. Wat Tham Pla School , Mae Sai , Chiang Rai: CUMZ 3913, 4844, 10189. Tham Mae Suai , Mae Suai , Chiang Rai: CUMZ 3907, 4345, 4807 (Fig. 31E, F ). Khao Tham Phra , Muang , Chiang Rai: CUMZ 3915, 4795 (Fig. 31D ), 4797, 4839, 4890, 10187. Wat Pha Cha Lui , Pa Dad , Chiang Rai: CUMZ 4435. Wat Tham Phra Bumpenboon , Phan , Chiang Rai: CUMZ 3914, 4495, 4496, 4706, 4846, 10027, 10034. Ban Pang Ma Yao , Chiang Dao , Chiang Mai: CUMZ 10185. Tham Chiang Dao , Chiang Dao , Chiang Mai: CUMZ 3911, 4438, 4499, 4881, 10181, 10182, 10183, 10192. Tham Brichinda , Chom Thong , Chiang Mai: CUMZ 10195. Huai Mae Muk Waterfall , Fang , Chiang Mai: CUMZ 10184 .

Diagnosis.

Shell small to medium, slightly thin and depressed. Detached whorl medium in length, curved and descending. Breathing device tubular and usually attached to preceding whorl. Shell colour with dark brown zigzag patterns on both sides.

Differential diagnosis.

This new species differs from R. marioni , R. jalorensis , and R. thachi in having a brown zigzag colour pattern and short detached whorl. In contrast, these three species have uniformly brownish to dark brown shells (rarely with a blotched pattern) and long and twisted detached whorls. In addition, R. thachi has a broader expanded aperture on the palatal side, while R. trigrina sp. nov. has a thickened, slightly expanded, multi-layered lip.

Description.

Shell. Shell small to medium, cW 15.7-20.5 mm, cH 8.5-11.7 mm, slightly thin, and sub-discoidal to discoidal; detached-whorl length 4.5-13.5 mm. Apex acute and dark; spire convex to nearly flat. Whorls 4 to 5, convex, increasing regularly; suture wide and shallow; last whorl rounded and stout. Shell surface with fine growth lines. Periostracum thin, corneous, and transparent. Shell with brown to dark brown zigzag patterns and faded on ventral shell surface, with narrow, dark, spiral band on periphery. Detached whorl medium in length, approximately the same length as aperture width, curved and descending. Peristome circular and double; lip thickened, expanded and multi-layered. Aperture opened sub-ventrally. Breathing device tubular and curved or straight, and its tip usually attached to preceding whorl; outer lip forming a long and closed tube, and located just behind apertural lip; inner lip with hole inside aperture. Umbilicus widely opened and deep. Operculum calcareous, cup-shaped, and multispiral (Fig. 31 ).

Radula. Teeth arrangement and shape are similar to those of R. housei . Central tooth with triangular central cusp, flanked by two lateral cusps on each side, each pair with pointed tips. Lateral teeth composed of four cusps; central cusp large with dull tip and flanked by one outer and two inner cusps. Marginal teeth each consisting of three pointed cusps (Fig. 32F ).

Etymology.

The specific name tigrina comes from the Latin word tigris. It refers to the brownish streak or zigzag colour pattern on the shell surface of this new species, which is similar to the colour pattern of the Bengal tiger, Panthera tigris tigris (Linnaeus, 1758).

Distribution.

This species is mainly distributed in northern Thailand in Chiang Rai, Maehongsorn, and Chiang Mai provinces (Fig. 18 ).

Remarks.

This species has high variation in shell colour, from dark brown zigzag patterns to whitish shells without patterns (Fig. 31F ) among specimens from the same collection localities.

Figures

Figure 18. Distribution map of Rhiostoma housei - species group.

Figure 31. Shell of Rhiostoma tigrina sp. nov. A holotype CUMZ 4497 / 1 from Tham Pum Tham Pla, Mae Sai, Chiang Rai B paratype CUMZ 4497 / 2 from type locality C paratype CUMZ 4806 from type locality D specimen CUMZ 4795 from Tham Phra, Chiang Rai E, F specimens CUMZ 4807 Mae Suai, Chiang Rai

Figure 32. Radula morphology A Rhiostoma housei specimen CUMZ 3982 from Wat Tham Srivilai, Saraburi B Rhiostoma hainesi specimen from Chanthaburi C Rhiostoma jalorensis specimen CUMZ 3994 from Wat Tham Sua, Krabi D Rhiostoma ebenozostera sp. nov. paratype CUMZ 4704 from Tham Pha Poo, Loei E Rhiostoma lannaense sp. nov. paratype CUMZ 4701 from Chiang Dao, Chiang Mai F Rhiostoma tigrina sp. nov. paratype CUMZ 4497 / 2 from Mae Sai, Chiang Rai.