Rhiostoma jalorensis Sykes, 1903

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

publication ID	https://dx.doi.org/10.3897/zookeys.1142.90097
publication LSID	lsid:zoobank.org:pub:A1129EE5-0F99-41CF-B73A-E771B66E2486
persistent identifier	https://treatment.plazi.org/id/775B1D12-12E7-5CA5-AA0D-F4E622975446
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scientific name	Rhiostoma jalorensis Sykes, 1903
status

Treatment

9. Rhiostoma jalorensis Sykes, 1903

Figs 17D View Figure 17 , 18 View Figure 18 , 26 View Figure 26 , 27 View Figure 27 , 32C View Figure 32

Rhiostoma jalorensis Sykes, 1903: 196, pl. 20, figs 6-8. Type locality: Limestone hills and caves, Biserat, Jalor [=Yala Province, Thailand]. Salisbury 1949: p1. 3B, figs 1, 2. Tumpeesuwan 2001: 47-52, figs 4.13-4.15. Tarruella and Doménech 2010: 190, fig. 2a, b. Kongim et al. 2013b: 16, fig. 2h.

Rhiostoma jalorense - Laidlaw 1928: 31.

Rhiostoma cf. smithi - Hemmen et al. 1999: 10, 11, figs 7, 9, 10 (misidentified).

Rhiostoma smithi - Hemmen and Hemmen 2001: 38, fig. 4 (misidentified). Patamakanthin 2001: 222, 223, figs f1-f3, i1-i4, j1-j4, l1-l3 (misidentified).

Rhiostoma huberi Thach, 2018: 17, figs 68-70. Type locality: Ao Luc, South Thailand [Ao Luek District, Krabi Province]. New synonym.

Type material.

Holotype UMZC I.100155 (Fig. 26A View Figure 26 ) from Biserat, State of Jalor, Malay Peninsula and paratype NMW 2.1981.118.02760 (1 shell; Fig. 26B View Figure 26 ). Holotype MNHN-IM-2000-34049 (Fig. 26C View Figure 26 ) of Rhiostoma huberi Thach, 2018, from Ao Luc, South Thailand.

Other material examined.

Thailand: Klong Seang Wildlife Sanctuary, Ban Ta Khun, Surat Thani: CUMZ 4323. Nature Trail, Khaosok, Ban Ta Khun, Surat Thani: CUMZ 4478, 4723. Ratchaprapha Dam, Ban Ta Khun, Surat Thani: CUMZ 4894. Anurak Resort, Panom, Surat Thani: CUMZ 10142. Tham Nam Lod, Panom, Surat Thani: CUMZ 10145. Ao Phang-nga, Muang, Phang Nga: CUMZ 4327. Khao Prao, Muang, Phang Nga: CUMZ 4327. Phang-nga Bay, Muang, Phang Nga: CUMZ 4325, 4326. Wat Tham Suwannakhuha, Takua Thung, Phang Nga: CUMZ 3837, 3848, 4328, 4329, 4821, 4843 (Fig. 27A-C View Figure 27 ). Tham Nam Pud, Muang, Phang Nga: CUMZ 3836, 3839, 3841, 3899, 4387 (Fig. 26F View Figure 26 ), 10136. Tham Kiriwong (Tham Kob), Thap Put, Phang Nga: CUMZ 3822, 3823, 3832, 4484, 4485, 4850, 10143. Tao Thong Waterfall, Thap Put, Phang Nga: CUMZ 3817, 3829, 3845, 4386, 4482, 4483 (Fig. 27D-F View Figure 27 ), 4798, 4837, 4858, 4873, 10141. On the way to Than Bok Khorani, Ao Luek, Krabi: CUMZ 10144, 10146. Tham Na Mee , Ao Luek, Krabi: CUMZ 10137. Tham Phet, Ao Luek, Krabi: CUMZ 3831. Tham Sra Yoon Thong, Ao Luek, Krabi: CUMZ 3819. Tham Chang Sri, Muang, Krabi: CUMZ 4330. Tham Lang Rong Rian, Ban Tubprik Primary School, Muang, Krabi: CUMZ 4487. Wat Tham Sua, Muang, Krabi: CUMZ 3834, 3994 (Figs 17D View Figure 17 , 26D, E View Figure 26 ), 4331, 4486, 4859, 10138, 10139, 10140 .

Diagnosis.

Shell medium, thick and depressed. Detached whorl long, curved and descending. Breathing device tubular. Shell colour usually uniformly brown to dark brown and with or without peripheral band.

Differential diagnosis.

Rhiostoma jalorensis can be distinguished from R. ebenozostera sp. nov. in having longer detached whorl, uniformly dark brown shell colour, and narrow peripheral band. In contrast, the new species has a shorter detached whorl, dark brown blotches shell colour, and with broad and dark brown peripheral band. In addition, the geographically disjunct distributions suggest that they are distinct species.

Description.

Shell. Shell small to medium, cW 17.1-20.6 mm, cH8.8-11.8 mm, slightly thick, and sub-discoidal shape; detached-whorl length 12.5-19.5 mm. Apex acute; spire slightly elevated. Whorls 5 to 6, convex, increasing regularly; suture wide and deep; last whorl rounded. Shell surface with fine growth lines. Shell colour uniformly brown, dark brown to black (rarely with zigzag pattern); ventral shell surface with paler colour; thin and narrow peripheral band sometimes present. Periostracum thick or thin corneous and transparent. Aperture opened sub-ventrally to ventrally. Detached whorl long, ~ 2 × longer than apertural width, curved and descending. Peristome circular and double; lip thickened, expanded, and multi-layered. Breathing device tubular, straight and its tip usually attached to preceding whorl (sometimes not attached); outer lip forming a long, straight and closed tube, and located just behind apertural lip; inner lip with small hole inside aperture. Umbilicus widely opened and deep. Operculum calcareous, cup-shaped, and multispiral (Figs 26 View Figure 26 , 27 View Figure 27 ).

Radula. Teeth arrangement and shape are similar to R. housei . Central tooth with large central cusp and two lateral cusps on each side. Lateral teeth composed of four cusps; central cusp large and triangular; two inner cusps with pointed tips and tapering in size; one outer cusp small. Marginal teeth each composed of three cusps (Fig. 32C View Figure 32 ).

Distribution.

The previous records of this species were from the type locality, Biserat, Jalor (former name of Yala Province, Thailand). The records from Koh Si-Hah, Singgora (now in Phatthalung Province, Thailand) by Laidlaw (1928) and Salisbury (1949) need to be verified with new collections. The recent collections are mainly from the western part of peninsular Thailand in Surat Thani, Phang Nga and Krabi provinces (Fig. 18 View Figure 18 ).

Remarks.

Rhiostoma jalorensis tends to have high variation in both shell form and shell colour. For example, the specimens from Tham Nam Pud, Phang Nga (Fig. 26F View Figure 26 ) exhibit relatively large shells with long and descending detached whorl (dL = 12.0-25.0 mm, 19.28 ± 3.43 mm), dark shell colour, and aperture opened sub-ventrally to ventrally. On the other hand, the population from Wat Suwankuha, Phang Nga (Fig. 27A-C View Figure 27 ) tend to have small shells with short detached whorl (dL = 9.0-14.5 mm, 11.67 ± 1.31 mm), pale brown to dark shell colour, and aperture opened sub-laterally. The specimens from Tao Tong Waterfall, Phang Nga (Fig. 27D-F View Figure 27 ) have medium to long descending detached whorl, brownish shell colour, and aperture opened sub-ventrally. However, the unique attributes of descending detached whorl, tubular-shaped breathing device and monochrome brown to black shell colour suggest that these are morphological variations.

The holotype of Rhiostoma huberi Thach, 2018 from Krabi Province is in an early stage of maturation, as the shell has a thin and sharp apertural lip. This specimen has a long and descending detached whorl, a brownish zigzag pattern on the coiled whorl, tubular-shaped breathing device, and aperture opened ventrally. In the absence of continuous characters in other populations, this extreme example would undoubtedly be recognised as a distinct species. However, the COI analysis clearly suggests that specimens from the entire distribution range and with these shell variations belong to a single species (Fig. 3 View Figure 3 ). Therefore, we formally synonymise Rhiostoma huberi Thach, 2018 with R. jalorensis .