Rhiostoma housei (Haines, 1855)

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

4. Rhiostoma housei (Haines, 1855)

Figs 17A , 18 , 19 , 20 , 32A

Cyclostoma housei Haines, 1855: 157, pl. 5, figs 12-15. Type locality: Siam [= Thailand]. Boyko and Cordeiro 2001: 52.

Pterocyclos housei - Pfeiffer 1858: 29. Reeve 1863: Pterocyclos pl. 4, species 21.

Rhiostoma housei - Benson 1860: 97. Pfeiffer 1862a: 117, pl. 12, fig. 9. Pfeiffer 1865: 38. Martens 1867: 63. Fischer 1891: 101. Möllendorff 1894: 152. Kobelt and Möllendorff 1897: 115. Kobelt 1902: 178. Fischer and Dautzenberg 1904: 427. Kobelt 1911: 757, 758, pl. 110, figs 8-10, pl. 113, fig. 2. Zilch 1956: 174. Rees 1964: 67, pl. 4, fig. 15. Solem 1966: 11. Fischer 1973: 47. Abbott 1989: 29, 42, with 3 figures. Tumpeesuwan 2001: 41-46, figs 4.10-4.12. Kongim et al. 2013b: 16, fig. 2f, g.

Rhinostoma [sic] Rhinostoma housei - Habe 1965: 128 (in part), pl. 2, fig. 10.

Pterocyclos (Spiraculum) housei - Martens 1860: 10.

Pterocyclus [sic] ( Rhiostoma ) Rhiostoma housei - Nevill 1878: 263.

Cyclostoma (Pterocyclos) housei - Boyko and Cordeiro 2001: 52.

Type material.

This species was described from specimens from the Haines collection (AMNH). The unique name-bearing type was not designated; however, at least two specimens were illustrated in the original description. The specimen identical to the illustration (shape of breathing device) and measurements in Haines (1855: figs 12, 13) is figured herein, syntype AMNH 42923 (5 shells; Fig. 19A, B ) from Siam [Thailand].

Other material examined.

Thailand: Boong Tuey, East Siam: RBINS 659990, 659991; Pak Chong, East Siam: RBINS 659978, 659979, 659980; Lam Ton Lang, East Siam : RBINS 659982, 659983, 659984. Siam: NHMW 75000/E/23126 (1 shell). Samui, Siam: NHMW Rusnov (1 shell). Tham Phet Tham Thong, Takhli, Nakhonsawan: CUMZ 4385. Pukae Botanical Garden, Chaloem Phra Kiat, Saraburi: CUMZ 4742. Wat Tham Srivilai, Chaloem Phra Kiat, Saraburi: CUMZ 3982 (Figs 7A-C , 19D , 20 , 32A ), 4449. Kaeng Khoi, Saraburi: CUMZ 4315. Ban Tha Sao Village , Kaeng Khoi, Saraburi: CUMZ 10135. Wat Tham Phra Phothisat, Kaeng Khoi, Saraburi: CUMZ 10026, 10158. Chet Sao Noi Waterfall, Muaklek, Saraburi: CUMZ 4732. Muaklek, Saraburi: CUMZ 4390, 4460. Wat Tham Dao Khao Kaew, Muaklek, Saraburi: CUMZ 3802, 3934, 4389, 4760, 4842, 4897, 10131, 10133. Khao Sompod, Chai Ba Dan, Lopburi: CUMZ 3932, 3936, 3937. Wat Tham Promlok, Chai Ba Dan, Lopburi: CUMZ 10128. Sub Langka, Lamsonthi, Lopburi: CUMZ 4736. Khao Look Chang, Pak Chong, Nakhon Ratchasima: CUMZ 3805, 3981, 4316, 4318, 4320, 4379, 4384 (Fig. 19E ), 4454. The way to Khao Yai, Pak Chong, Nakhon Ratchasima: CUMZ 4454. Wat Tham Prommachan Thammaram, Pak Chong, Nakhon Ratchasima: CUMZ 10160. Wat Tham Sub Muet, Pak Chong, Nakhon Ratchasima: CUMZ 10132. Wat Tham Thep Nimit, Pak Chong, Nakhon Ratchasima: CUMZ 10126. Wat Thepphitak Punnaram, Pak Chong, Nakhon Ratchasima: CUMZ 4321, 4416. Sakaerat Biosphere, Pak Thong Chai, Nakhon Ratchasima: CUMZ 4391. Sakaerat Environmental Research Station , Wang Nam Khiao, Nakhon Ratchasima: CUMZ 10134. Ban Bueng, Ban Bueng, Chonburi: CUMZ 4312. Khao Chakan, Srakeo: CUMZ 10156. Khao Nang Panturat, Cha Am, Phetchaburi: CUMZ 4879 (Fig. 19F ), 10129, 10130, 10164, 10165. Khao Nang Panturat Nature Reserve , Cha Am, Phetchaburi: CUMZ 4480. Tham Na Kwang , Cha Am, Phetchaburi: CUMZ 3988, 4452, 4719, 10162. 30 km. before Pa La Au Waterfall , Hua Hin, Phetchaburi: CUMZ 3827, 4740. Kaeng Kachan, Phetchaburi: CUMZ 4409, 4412. Khao Lom Muak, Muang, Prachuap Khiri Khan: CUMZ 3870, 3987 (Fig. 17A ), 4322, 10163. Bang Poo, Sam Roi Yod, Prachuap Khiri Khan: CUMZ 4414, 4417, 4429, 4430. Saun Wiweg Bureau of Monks , Sam Roi Yod, Prachuap Khiri Khan: CUMZ 10127. Ao Noi, Prachuap Khiri Khan: CUMZ 3868. Tham Pissadarn, Tha Sae, Chumphon: CUMZ 4383 (Fig. 19C ), 4453, 4851 .

Diagnosis.

Shell medium to large, thick, and depressed. Detached whorl longer than aperture width, curved, and descending. Breathing device straight with complete tube. Shell usually with dark brown zigzag patterns.

Differential diagnosis.

Rhiostoma housei can be distinguished from R. tigrina sp. nov. in usually having a stout detached whorl, generally a curved tubular breathing device, and a faded colour pattern. In contrast, R. tigrina sp. nov. has a slender detached whorl, generally a straight tubular breathing device, and a brownish zigzag colour pattern.

Description.

Shell. Shell medium to large, cW 22.1-26.4 mm, cH 12.1-13.8 mm, thick, and sub-discoidal to discoidal shape; detached-whorl length 8.0-14.5 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 thin corneous, and transparent to thick with brownish colour. Shell colour whitish with dark brown zigzag pattern; dorsal shell surface with darker colour pattern than ventral surface; with narrow brownish spiral band on periphery (sometimes absent). Detached whorl of medium length, approximately the same as apertural width. Peristome circular and double; lip thickened, slightly expanded and multi-layered. Aperture opened sub-laterally. Breathing device tubular and its tip usually attached to preceding whorl; outer lip forms a long, curved or straight, closed tube; inner lip with small hole inside aperture. Umbilicus widely opened and deep. Operculum calcareous, tall cup-shaped, and multispiral (Fig. 19 ).

Radula. Taenioglossate radula arranged in inverted V-shaped rows. Central tooth with well-developed central cusp and two lateral cusps on each side tapering in size; central cusp large with blunt tip; lateral cusps with triangular shape and pointed tip. Lateral teeth consisting of four cusps; central cusp large, elongate, and flanked by pointed tips of two small inner cusps and one outer cusp. Inner and outer marginal teeth each composed of three cusps; central cusp with large and dull tip, flanked by small pointed tips of one inner cusp and one outer cusp (Fig. 32A ).

Distribution.

The type locality was given as a broad location of “Siam”; however, the specimens from central Thailand are the most similar to the syntype illustrated herein (Fig. 19A, B ). In this study, R. housei has a wide distribution ranging from central to peninsular Thailand. The southernmost limits are around the Isthmus of Kra (Pratiew, Chumphon Province), and the northern limit is approximately in Nakhon Sawan Province (Fig. 18 ).

Remarks.

Previous literature recorded R. housei from several places in Laos, Cambodia, and Vietnam [Tonkin] ( Möllendorff 1885; Ancey 1898; Fischer 1973). However, these records seem ambiguous because the type specimens have never been examined, were very limited in the number of specimens, and many species have a similar shell morphology to R. housei . Moreover, the species delimitation by previous authors is probably different from the concept of the type specimens. For example, this species has been reported in Chiangdao, Chiangmai, northern Thailand (sensu Solem 1966). We collected many specimens from several populations in the same area and examined Solem’s specimens in ZMUC. Due to the clear differences in shell characters, we recognise these populations as distinct species ( R. tigrina sp. nov.). For that reason, the distribution range of R. housei , especially from Laos, Cambodia, and Vietnam, needs to be re-examined with new specimen collections with more precise locality.

Do et al. (2020b) reported several " R. housei " populations from Northern Vietnam in Dien Bien, Hao Binh, and Son La provinces. The figured specimen from Dien Bien Province shows the distance ~800 km away from the central population of this species from central Thailand. This specimen ( Do et al. 2020b: fig. 6b, c) had a depressed spire, and a curved, tubular breathing device, and is probably R. simplicilabre rather than R. housei .

The specimens collected from southern Thailand (Chumporn, Phetchaburi, and Prachuapkhirikhan provinces) tended to have longer detached whorls, longer breathing devices, and brighter shell colour than the populations from central Thailand (typical). However, the shell colour pattern, detached whorl, and breathing device structures are identical to the type specimens (Fig. 19A, B ). Therefore, these are attributed to morphological variation across the wide distribution range of this species.

Figures

Figure 7. A-C Internal anatomy of Rhiostoma housei specimen CUMZ 3982 from Tham Sriwilai, Saraburi, A inside view of lung cavity shows an arrangement of the kidney, circulatory system and the terminal part of the digestive tract B male genitalia and C female genitalia D spermatophore of Rhiostoma samuiense specimen CUMZ 4713 from Kanchanadit, Surat Thani with its cross sections showing spermatophore shape in each position. Abbreviations: an, anus; bc, bursa copulatrix; fc, faeces; go, genital opening; h, heart; kd, kidney; mc, mantle collar; od, oviduct; pg, prostate gland; re, rectum; sr, seminal receptacle; ut, uterus; v, vein; vd, vas deferens.

Figure 17. Live snails of the species group II A Rhiostoma housei specimen CUMZ 3987 from Ao Manow, Prachuap Khiri Khan B, C Rhiostoma hainesi from Khao Soi Dao, Chanthaburi B without breathing device and C with long breathing device D Rhiostoma jalorensis specimen CUMZ 3994 from Wat Tham Sue, Krabi. All figures are not to scale. Photographs: P. Tongkerd (B, C).

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

Figure 19. Shell of Rhiostoma housei A, B syntype AMNH 42923 from Siam A figured specimen in Haines (1855: figs 12, 13) anb B other specimen from the same syntype lot C specimens CUMZ 4383 from Tham Phitsadan, Chumphon D specimen CUMZ 3982 from Tham Sriwilai, Saraburi E specimen CUMZ 4384 from Pak Chong, Nakhon Ratchasrima F specimen CUMZ 4879 from Hua Hin, Prachuap Khiri Khan.

Figure 20. Drawing of general anatomy of Rhiostoma housei specimen CUMZ 3982 from Saraburi Province, Thailand. A female B male. Abbreviations: bc, bursa copulatrix;; cm, columellar muscle; ct, cephalic tentacle; dg, digestive gland; es, eyespot; f, foot; fc, faeces; int, intestine; lc, lung cavity; mc, mantle collar; od, oviduct; op, operculum; ov, ovary; p, external penis; pg, prostate gland; sg, sperm groove; sn, snout; te, testis; ut, uterus; vd, vas deferens; vg, vaginal groove.

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.