Rhiostoma dalyi Blanford, 1902

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

8. Rhiostoma dalyi Blanford, 1902

Figs 18 , 25

Rhiostoma dalyi Blanford, 1902: 34, 35, fig. 1. Type locality: Juxta Phitsanulok, in sylvis humidis etr densis [Phitsanulok Province, Thailand]. Blanford 1903: 281. Fischer and Dautzenberg 1904: 427. Solem 1966: 11. Sutcharit et al. 2019: 21, fig. 4i, j.

Rhiostoma housei - Tumpeesuwan 2001: 41-46, figs 4.10-4.12 (misidentified).

Type material.

Syntype NHMUK 1902.1.24.14-16 (3 shells; Fig. 25A ) from Pitsunaloke, Siam. This syntype lot in the Blanford ex. Daly collection consists of three specimens; the figured specimen in the original description can be recognised by its curved breathing device and is figured herein.

Other material examined.

Thailand: Tham Pha Dang, Chiangkham, Phayao: CUMZ 4462, 4729. Doi Phunang, Dokkamtai, Phayao: CUMZ 3938, 3942, 4313, 4319, 4420. Tarnsawan Waterfall, Dokkamtai, Phayao: CUMZ 3824, 3826, 3977 (Fig. 25D ). Tham Pha Tangyai, Pong, Phayao: CUMZ 3926 (Fig. 25E, F ), 4784. Tham Pha Tung, Pong, Phayao: CUMZ 10062. Ban Tha Sri, Muang, Lampang: CUMZ 4728. Pratupha, Ngoaw, Lampang: CUMZ 4463. 3 km. before the junction to Tham Sereethai, Long, Prae: CUMZ 4450. Hill Near Tham Air Tammachard, Long, Prae: CUMZ 3979, 4451. Tham Air Thammachad, Ban Pan, Long, Prae: CUMZ 4762. Tham Erawan, Long, Prae: CUMZ 4792, 4848 (Fig. 25B, C ), 10063, 10064. Wat Tham Pha Nang Koy, Rong Kwang, Prae: CUMZ 3884, 3924, 4726 .

Diagnosis.

Shell large, thick, and depressed. Detached whorl medium in length, and slightly descending. Breathing device tubular, curved, and attached to preceding whorl. Shell whitish with brownish zigzag patterns.

Differential diagnosis.

This species is very similar to R. housei from central Thailand. The distinguishing characteristics of R. dalyi are a stout last whorl and a tubular-shaped breathing device that is short, curved and attached to the preceding whorl. In comparison, R. housei has a slender last whorl, and a long and straight tubular breathing device. In addition, this species also differs from R. trigina sp. nov. in having a stout and short detached last whorl, a short and curved tubular breathing device, and a ventral shell surface usually without a pattern. In contrast, R. trigina sp. nov. possesses a slender detached whorl, long and straight tubular breathing device, and usually with brown zigzag patterns on both sides.

Description.

Shell. Shell medium to large, cW 19.9-24.6 mm, cH 9.7-13.4 mm, thick, and discoidal shape; detached-whorl length 7.5-14.0 mm. Apex acute with dark colouration; spire slightly elevated. Whorls 5 to 6, convex and increasing regularly; suture wide and deep; last whorl rounded and stout. Shell surface with fine growth lines. Periostracum thick or thin corneous and transparent. Shell colour whitish with brownish zigzag pattern; ventral shell surface usually without pattern; with narrow and dark brown spiral band on periphery. Detached whorl of medium length, approximately the same length as apertural width. Peristome circular and double; lip thickened, slightly expanded and multi-layered. Aperture opened sub-laterally. Breathing device tubular, curved and its tip attached to preceding whorl; outer lip forming a short 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. 25 ).

Distribution.

This species is distributed in the northern part of Thailand in Phitsanuloke (type locality), Lampang, Phrae and Phayao provinces (Fig. 18 ).

Remarks.

Solem (1966) record the specimens from 'Chieng Dao’ as this species. However, we examined a number of specimens from Chieng Dao, Chieng Mai Province and found clearly distinct shell morphology compared to the type specimen of R. dalyi . In addition, the COI barcoding suggests that R. dalyi and R. trigina sp. nov. are separate species (Fig. 3 ). Therefore, the record of this species by Solem (1966) should be referred to R. trigina sp. nov.

Figures

Figure 3. Maximum likelihood (ML) tree showing the relationships among Rhiostoma species based on 660 bp of the mitochondrial COI gene sequence. The major nodes are indicated by numbers as the Maximum likelihood (ML) bootstrap values and Bayesian posterior probabilities of Bayesian inference (BI), respectively. Nodes with sufficient support by both ML and BI are indicated by black circles, and nodes with partial support by only ML are indicated by grey circles, and only BI by white circles. Newly described species in this study are highlighted in blue.

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

Figure 25. Shell of Rhiostoma dalyi A syntype NHMUK 1902.1.24.14 - 16 from Juxta Phitsanulok B, C specimens CUMZ 4848 from Tham Erawan, Long, Prae D specimen CUMZ 3979 from Tarnsawan Waterfall, Phayao E, F specimens CUMZ 3926 from Tham Pha Tangyai, Pong, Phayao.