Rhiostoma strubelli Moellendorff , 1899

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

15. Rhiostoma strubelli Moellendorff, 1899

Figs 34 , 36 , 41B

Rhiostoms strubelli Möllendorff, 1899: 166. Type locality: Kalow, 5000', südliche Shan Staaten [Kalaw, Taunggyi District, Shan State, Myanmar]. Kobelt 1902: 179. Kobelt 1911: 763, pl. 113, fig. 11. Zilch 1956: 174.

Type material.

The original description did not explicitly indicate the number of specimens, and was without illustration or explicit designation of the name-bearing type, although one set of measurements was given in Möllendorff (1899). Later, Kobelt (1911: pl. 113, fig. 11) illustrated this species for the first time, and then Zilch (1956) recognised this figured specimen (SMF 130513) as the “holotypus”. This SMF collection lot contains only one specimen; therefore, the subsequent use of the term “holotypus” in Zilch (1956) constitutes a valid lectotype designation. Lectotype (designation in Zilch (1956)) SMF 130513 (Fig. 36A ) from S-Shan Staaten: Kalow, 5000'.

Other material examined.

China: Xishuangbanna Tropical Botanical Garden, Mengla County, Xishuangbanna Prefecture, Yunnan Province: CUMZ 10047 (7 shells; Fig. 36F ). Laos: Khao Pa Huak, Vieng Phuka District, Luang Nam Tha Province: CUMZ 10200 (29 shells; Figs 36B-E , 42B ).

Diagnosis.

Shell small, thin, and depressed; detached whorl shorter than apertural width. Shell with brownish zigzag patterns. Breathing device short and incomplete tube shape.

Differential diagnosis.

Rhiostoma strubelli can be distinguished from R. haughtoni and R. tigrina sp. nov. by having a smaller shell, very short detached whorl, incomplete tubular shape of breathing device, and apex with dark colouration. In contrast, R. haughtoni has a canal-shaped breathing device with a monochrome shell, while R. tigrina sp. nov. has a long, detached whorl and short to long breathing device with complete tube shape.

Description.

Shell. Shell small, cW 17.3-22.9 mm, cH 8.5-12.0 mm, thin, and sub-discoidal shell; detached-whorl length 2.0-7.0 mm. Apex acute and dark colouration; spire slightly elevated. Whorls 4 to 5, convex, increasing regularly; suture wide and shallow; last whorl rounded. Shell surface with fine growth lines. Periostracum thin, corneous, and transparent. Shell colour with brown zigzag pattern, and narrow dark brown spiral band on periphery. Detached whorl shorter than apertural width. Peristome circular and double; lip thickened and slightly expanded. Aperture opened sub-laterally. Breathing device with incomplete tube shape; outer lip protruded into a nearly closed tube; inner lip with deep incision or small hole inside aperture. Umbilicus widely opened and deep. Operculum calcareous, low cup-shaped, and multispiral (Fig. 36 ).

Radula. Teeth arrangement and shape are similar to R. asiphon . Central tooth with large central cusp and two lateral cusps on each side. Lateral teeth having four cusps; central cusp large, triangular, and flanked by two small inner cusps and one outer cusp. Marginal teeth each consisting of three pointed cusps (Fig. 42B ).

Distribution.

This species is known from Kalaw, Shan State, Myanmar. This study recorded specimens from Luang Namtha Province, Laos, and Yunnan in China (Fig. 34 ).

Remarks.

This species is previously known only from the holotype from the south of Shan State, Myanmar, which is close to northern Thailand and Laos. However, no Rhiostoma specimens collected from northern Thailand could be identified as this species. The specimen from Luang Namtha Province, Laos and Yunnan Province, China are very similar to the lectotype in having short detached whorl and breathing device with an incomplete tube shape. The only difference is in having darker irregular blotches on the shell than the type specimen, and this is considered as intrapopulation variation.

Figures

Figure 34. Distribution map of Rhiostoma asiphon - species group.

Figure 36. Shell of Rhiostoma strubelli A lectotype SMF 130513 from S-Shan Staaten: Kalow B-E specimens CUMZ 10200 from Vieng Phuka, Luang Namtha, Laos and E with long breathing device F specimen CUMZ 10047 from Xishuangbanna Botanical Garden, Yunnan, China.

Figure 41. Shell of Rhiostoma platymorpha sp. nov. A holotype CUMZ 4498 / 1 from Tham Muang On, Mae On, Chiang Mai B paratype CUMZ 4763 from type locality C, D paratypes CUMZ 4498 / 2 from type locality E, F specimens CUMZ 4783 from Tham Bua Tong, Mae Tang, Chiang Mai (with F albinistic shell form).

Figure 42. Radula morphology A Rhiostoma asiphon CUMZ 4826 from Angthong Islands, Surat Thani B Rhiostoma strubelli specimen CUMZ 10200 from Vieng Phuka, Luang Namtha, Laos C Rhiostoma breviocollar sp. nov. paratypes CUMZ 4491 from type locality D Rhiostoma anceyi sp. nov. paratype CUMZ 4494 / 2 from type locality E Rhiostoma furfurosum sp. nov. paratype CUMZ 4705 / 2 from type locality F Rhiostoma platymorpha sp. nov. paratype CUMZ 4763 from type locality.