Rhiostoma furfurosum Tongkerd & Panha, 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

19. Rhiostoma furfurosum Tongkerd & Panha sp. nov.

Figs 34 , 40 , 42E

Rhiostoma sp. 3- Tumpeesuwan 2001: 71-75, figs 4.25-4.27.

Rhiostoma sp. 4- Tumpeesuwan 2001: 76-81, figs 4.28-4.30 (in part).

Type material.

Holotype CUMZ 4705/1 (cW 23.2 mm, cH 13.1 mm, dL 9.5 mm; Fig. 40A ). Paratypes CUMZ 3901 (37 adults + 3 juveniles), CUMZ 3903 (105 adults + 11 juveniles), CUMZ 3904 (105 adults + 8 juveniles), CUMZ 3905 (200 adults + 14 juveniles), CUMZ 4447 (81 adults + 2 juveniles), CUMZ 4705/2 (6 shells; Figs 40B, C , 42E ), CUMZ 4833 (51 adults + 4 juveniles), CUMZ 4835 (5 shells), CUMZ 4884/1 (70 adults + 2 juveniles), CUMZ 10151 (1 shell), CUMZ 10152 (8 shells), NHMUK 20220444 (5 shells), and SMF 368679 (5 shells). All paratypes are from the type locality.

Type locality.

Tham Wang Dang, Noern Maprang District, Phitsanulok (16°41'40.1"N, 100°40'42.5"E). Limestone hill with dry dipterocarp forest and surrounded by paddy fields.

Other material examined.

Thailand: Pa Ma Muang Bureau of Monks , Noern Maprang, Phitsanulok: CUMZ 3980 (Fig. 40D, E ), 4446, 4885, 10023, 10148, 10149, 10150, Tham Bot Wang Na, Noern Maprang, Phitsanulok: CUMZ 10153. Tham Pha Tha Phol, Noern Maprang, Phitsanulok: CUMZ 4359, 4869, 10024. Tham Tao, Noern Maprang, Phitsanulok: CUMZ 3902. Tham Wang Thong, Noern Maprang, Phitsanulok: CUMZ 10147. Wat Ban Mung, Noern Maprang, Phitsanulok: CUMZ 10154. Wat Tham Muang, Noern Maprang, Phitsanulok: CUMZ 4356. Wat Tham Rue-si Mongkon, Srithep, Phetchabun: CUMZ 10016. Phu Keiw Wildlife Sanctuary, Phu Khiao, Chaiyaphum: CUMZ 4314, 4317, 4353 (Fig. 40F ). Tham Saeng Wiset Monastic Residence, Takfa, Nakhonsawan: CUMZ 10018, 10030. Wat Tham Khao Chaithong, Takfa, Nakhonsawan: CUMZ 10161 .

Diagnosis.

Shell medium, thick, and depressed; detached whorl shorter than apertural width. Shell colour brownish with dark brown zigzag patterns. Breathing device incomplete tube-shaped, and usually perpendicular to detached whorl.

Differential diagnosis.

Rhiostoma furfurosum sp. nov. differs from R. breviocollar sp. nov. by having a relatively larger shell size, and thickened and expanded apertural lip, whereas R. breviocollar sp. nov. has relatively smaller shell size, and apertural lip thickened and multi-layered.

Description.

Shell. Shell medium, cW 21.7-24.7 mm, cH 11.1-13.9 mm, thickened, and sub-discoidal to discoidal shape; detached-whorl length 5.0-9.5 mm. Apex acute with dark colouration; spire elevated. Whorls 5 to 6, convex, increasing regularly; suture wide and depressed; last whorl rounded and slender. Shell surface with fine growth lines. Shell colour with brownish to reddish brown zigzag pattern and ventral surface with paler colour pattern or sometimes with uniformly brownish colour; narrow dark spiral band on periphery. Periostracum thick corneous and brown. Detached whorl shorter than apertural width. Peristome circular and double; lip thickened, expanded, and multi-layered. Breathing device short to long with incomplete tube shape and usually perpendicular to detached whorl; outer lip forming a short to long and nearly closed tube; inner lip with deep incision. Operculum calcareous, low cup-shaped, and multispiral (Fig. 40 ).

Radula. Teeth arrangement and shape are similar to those of R. asiphon . Central tooth with large central cusp and two lateral cusps on each side tapered in size. Lateral teeth consisting of three cusps; inner cusp relatively small with pointed tip; outer cusp large with dull tip. Marginal teeth each consisting of three pointed cusps (Fig. 42E ).

Etymology.

The species name furfurosum comes from the Latin, meaning like bran or brownish. Thus, it refers to the prominent brownish shell colour of this new species.

Distribution.

This new species was found only in small, isolated limestone hills in Phitsanulok, Chaiyaphum, and Phetchabun provinces (Fig. 34 ).

Remarks.

Shell variation can be observed by the shell colour ranging from monochrome reddish brown to brown zigzag patterns. Furthermore, the shape of the breathing device varies from incomplete tubular to canal-shaped. In addition, the specimens from Phu Kiew, Chaiyaphum (Fig. 40F ) exhibit a lack of detached whorl, canal-shaped breathing device (rarely with short incomplete tube breathing device) attached to the preceding whorl, and with a dark brown zigzag pattern on both sides of the shell. However, we recognise this as variation resulting from an isolated population, while the similarities to R. furfurosum sp. nov. suggest that is the same species. Their shell morphologies are clearly distinct from other known species recorded in the adjacent areas.

Figures

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

Figure 40. Shell of Rhiostoma furfurosum sp. nov. A holotype CUMZ 4705 / 1 from Tham Wang Dang, Noern Maprang, Phitsanulok B, C paratypes CUMZ 4705 / 2 from type locality D, E specimens CUMZ 3980 from Pa Ma Muang, Noern Maprang, Phitsanulok F specimen CUMZ 4353 from Phu Khiao, Chaiyaphum.

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.