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

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/B0184368-8BD9-5701-858B-3AA8CADA8447
treatment provided by	ZooKeys by Pensoft
scientific name	Rhiostoma morleti Dautzenberg & Fischer, 1906
status

Treatment

23. Rhiostoma morleti Dautzenberg & Fischer, 1906 View in CoL

Figs 43A View Figure 43 , 44 View Figure 44 , 46 View Figure 46 , 47 View Figure 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 View Figure 46 ) 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 View Figure 46 ) from Ha-Giang. Syntype MNHN-IM-2000-33838 (1 shell; Fig. 46C View Figure 46 ) from Ha-Giang. Syntype RBINS-MT-658845 (2 shells; Fig. 46D View Figure 46 ) 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 View Figure 46 ). Kraisorn Cave , Vieng Xai District , Houaphanh Province, Laos: CUMZ 10002/1 (15 shells; Fig. 47B, C View Figure 47 ), 10002/2 (2 shells; Fig. 47A View Figure 47 ). Km 31, Vieng Xai District , Houaphanh Province: CUMZ 10003 (7 shells; Fig. 47D View Figure 47 ). Tam Xang (cave), Mueng Kham District , Xiangkhouang Province, Laos: CUMZ 10209 (4 shells; Fig. 47E, F View Figure 47 ) . 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 View Figure 46 , 47 View Figure 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 View Figure 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.