Rhiostoma cochinchinensis (Pfeiffer, 1857)

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

21. Rhiostoma cochinchinensis (Pfeiffer, 1857)

Fig. 45A

Cyclostoma (Opisthoporus) cochinchinense Pfeiffer, 1857 [1856]: 337. Type locality: Cochinchina [south of Vietnam].

Opisthoporus cochinchinensis - Pfeiffer 1858: 28. Fischer 1891: 100. Kobelt and Möllendorff 1897: 118.

Pterocyclos cochinchinensis - Reeve 1863: Pterocyclos , pl. 4, species 22.

Cyclotus cochinchinensis - Kobelt 1902: 209. Sutcharit et al. 2019: 19, fig. 4d.

Type material.

Probable syntype NHMUK 20170354 (1 shell; Fig. 45A ) from Cochin China.

Diagnosis.

Shell flattened and without detached whorl. Uniformly whitish to pale yellowish shell. Breathing device with incomplete tube shape. Operculum calcareous and low cup-shaped.

Differential diagnosis.

This species can be distinguished from R. asiphon , especially a yellowish shell form in having a flattened shell and incomplete tube shape. In comparison, R. asiphon has a sub-discoidal shell and notch-shaped breathing device.

Description.

Shell. Shell slightly thin and flattened, width 36.5 mm, height 12.5 mm. Apex acute; spire slightly elevated. Whorls 4, convex; suture deep; last whorl rounded and stout. Shell surface with fine growth lines. Periostracum corneous and transparent. Shell colour uniformly whitish to pale yellowish and without peripheral band. Breathing device with incomplete tube shape and attached to preceding whorl; detached whorl absent (or inconspicuous). Peristome circular and double; lip thickened and slightly expanded. Aperture opened sub-laterally; outer lip protruded and forming a nearly closed tube; inner lip with deep incision. Umbilicus widely opened. Operculum calcareous, cup-shaped, and multispiral (Fig. 45A ).

Remarks.

This species was described by Pfeiffer (1857) based on the Cuming collection. Subsequently, Reeve (1863) published the images and re-assigned it to the Pterocyclos . Later, Kobelt (1902) redescribed and placed this species into the genus Cyclotus , and this treatment has been followed since then. The probable syntype was recently found and illustrated (see Sutcharit et al. 2019). This specimen has a unique breathing device and calcareous cup-shaped operculum with elevated lamellae, suggesting that it is a member of the genus Rhiostoma . In addition, the uniformly whitish to pale yellowish shell without any dark brown bands or streaks of this specimen probably represents the albinistic form. However, we maintain this as a valid species despite no additional specimens, and have assigned it to the genus Rhiostoma .

The collection locality was from “Cochinchina” ( Pfeiffer 1857), which refers to the approximate area of southern Vietnam and southeast Cambodia. The recent land snail survey from southern Cambodia recovered no specimens ( Sutcharit et al. 2020), and an intensive survey in southern Cambodia and southern Vietnam is essential for clarifying the systematic status of this species.

Figures

Figure 45. Shell of Rhiostoma spp. A Rhiostoma cochinchinensis probable syntype NHMUK 20170354 from Cochinchina B-F Rhiostoma cambodjense B syntype NHMUK 1893.2.4.776 from Battambang, Cambodje C syntype of " Opisthoporus pulchellus Morlet, 1889 " MNHN-IM- 2000 - 9828 from Mount. Sisophon D specimen CUMZ 10203 / 2 from Thammaban Khiri, Serei Saophoan (Sisophon), Cambodia E, F specimens CUMZ 4714 from Khao Chakan, Srakeo. Photograph: A Robin and V Heros, MNHN (C).