Rhiostoma morleti Dautzenberg & Fischer, 1906

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

23. Rhiostoma morleti Dautzenberg & Fischer, 1906

Figs 43A , 44 , 46 , 47

Pterocyclos planorbulus Morlet, 1891: 247 (not Lamarck). Locality: Long-son [Lang Son Province, Vietnam].

Rhiostoma morleti Dautzenberg & Fischer, 1906: 429-431, pl. 10, figs 1-4. Type locality: Luang-Prabang, Laos; Ha Giang, Tonkin [Ha Giang Province, Vietnam]. Kobelt 1911: 755, 756, pl. 110, figs 1-4. Thach 2016: 38, fig. 125. Do et al. 2020b: 168, 169, fig. 1g-k.

Type material.

Syntype MNHN-IM-2000-20961 (1 shell; Fig. 46A ) from Laos, chaine de partage entre le Mékong et le Ménam (figured in Dautzenberg and Fischer 1906: pl. 10, figs 1, 2). Syntype MNHN-IM-2000-33837 (2 shells; Fig. 46B ) from Ha-Giang. Syntype MNHN-IM-2000-33838 (1 shell; Fig. 46C ) from Ha-Giang. Syntype RBINS-MT-658845 (2 shells; Fig. 46D ) from Not-Son, Tonkin.

Other material examined.

Laos: Ban Na Wid, Vieng Xai District, Houaphanh Province: CUMZ 10004/1 (20 shells), 10004/2 (3 shells; Fig. 46E, F ). Kraisorn Cave , Vieng Xai District , Houaphanh Province, Laos: CUMZ 10002/1 (15 shells; Fig. 47B, C ), 10002/2 (2 shells; Fig. 47A ). Km 31, Vieng Xai District , Houaphanh Province: CUMZ 10003 (7 shells; Fig. 47D ). Tam Xang (cave), Mueng Kham District , Xiangkhouang Province, Laos: CUMZ 10209 (4 shells; Fig. 47E, F ) . Vietnam: Phong-Tho, Tonkin: SMF 130576 (4 shells), RBINS 659868 (2 shells), 659871 (2 shells).

Diagnosis.

Shell large, flattened to depressed shell and without detached whorl. Breathing device incomplete or canal-shaped and pointed apically. Peristome double; outer lip with narrow canal; inner lip with shallow incision or small hole.

Differential diagnosis.

This species is similar to R. cochinchinense in general shell form, but with an incomplete tube or canal-shaped breathing device, generally brownish to whitish pattern and with a peripheral band, which are the distinguishing characters. In comparison, R. cochinchinense has an incomplete tube-shaped breathing device, a uniformly whitish shell, and lacks a peripheral band.

Description.

Shell. Shell usually large, width 18.9-28.1 mm, height 8.7-13.0 mm, thickened, and flattened shape. Apex acute; spire flat to slightly elevated. Whorls 4 to 5, convex, increasing regularly; suture narrow and deep; last whorl rounded and stout. Shell surface with fine growth lines. Periostracum thick corneous and brown. Shell colour varies from uniformly whitish or brownish pattern, with narrow to wide dark-brown spiral band on periphery. Detached whorl absent (rarely very short). Peristome circular and double; lip thickened and slightly expanded. Aperture opened sub-laterally. Breathing device incomplete or canal-shaped, protruding apically, and usually not attached to preceding whorl; outer lip protruded and with narrow canal or forming nearly closed tube; inner lip with shallow incision or small hole inside shell. Umbilicus widely opened. Operculum calcareous, cup-shaped, and multispiral (Figs 46 , 47 ).

Distribution.

The previous record of this species was from Luang Phrabang, Laos, and Ha Giang and Lang Son, North Vietnam ( Dautzenberg and Fischer 1906). Later records were reported from Ha Giang, Yen Bai, Son La, Lai Chau, and Dien Bien provinces, north Vietnam ( Do et al. 2020b). This study recorded specimens from several localities in Houaphanh Province, northern Laos (Fig. 44 ).

Remarks.

The identification of this species without the operculum might easily (and wrongly) place it into the genus Pterocyclos. Nevertheless, the unique calcareous cup-shaped operculum with elevated lamellae of the type specimen clearly indicates that it is Rhiostoma .

The two specimens figured in Do et al. (2015: fig. 4c, d) as R. morleti and Rhiostoma sp. have the tubular-shaped breathing device that is curved, and with tip attached to the preceding whorl. This character clearly differs from the typical R. morleti , but rather should be referred to as R. simplicilabre . The specimen figured in Inkhavilay et al. (2019) as R. morleti from Bolikhamxay, Laos, shows considerable difference from the type specimen and from the newly collected specimens from Houaphanh Province, northern Laos. Therefore, this study recognises it as R. laosense sp. nov.

Figures

Figure 43. Live snails of the species group IV A Rhiostoma morleti, from Vieng Xai, Houaphanh, Laos B Rhiostoma laosense sp. nov. from Hineboun, Khammouane, Laos. Photographs: K. Inkhavilay.

Figure 44. Distribution map of Rhiostoma morleti - species group.

Figure 46. Shell of Rhiostoma morleti A syntype MNHN-IM- 2000 - 20961 from chaine de partage entre le Mekong et le Menam B syntype MNHN-IM- 2000 - 33837 from Ha-Giang C syntype MNHN-IM- 2000 - 33838 from Ha-Giang D syntype RBINS-MT- 658845 from Not-Son, Tonkin E, F specimens CUMZ 10004 / 2 from Ban Na Wid, Vieng Xai, Houaphanh, Laos. Photograph: M Caballer and V Heros, MNHN (A-C).

Figure 47. Shell of Rhiostoma morleti A specimen CUMZ 10002 / 2 from Kraisorn Cave, Vieng Xai, Houaphanh, Laos B, C specimens CUMZ 10002 / 1 from Kraisorn Cave, Vieng Xai, Houaphanh, Laos D specimen CUMZ 10003 from Km 31, Vieng Xai, Houaphanh, Laos E, F specimen CUMZ 10209 from Tam Xang, Mueng Kham, Xiangkhouang, Laos.