Rhiostoma sp., 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

Rhiostoma sp.

Figs 54 , 55D-F

Material examined.

Laos: Khau Nam Nua, Vieng Xai District, Houaphanh Province: CUMZ 10050 (4 shells; Fig. 55D ). Ban Zox (village), Xaysetha District , Attapeu Province: CUMZ 10051 (7 shells; Fig. 55E, F ) .

Remarks.

There are two lots of empty shells collected from northern and southern Laos; these specimens have a depressed conical shape and a thickened shell, and the spire is nearly flat and dark in colour. Shell colour is uniformly purplish, with a narrow dark brown peripheral band and thin brownish periostracum. The detached whorl is approximately the same length or longer than aperture width, curved and descending. The aperture is rounded; the lip is thickened and expanded; the breathing device is a knob shape. These characters are nearly identical to the unique characters of R. samuiense from southern Thailand and peninsular Malaysia. As no obvious apomorphic characters of these disjunct populations (more than 1500 km apart) are available, future study (especially DNA phylogeny) will be needed to elucidate their systematic position. However, the populations from Laos were found from karst areas with primary forests and without human inhabitants, and therefore are not likely due to recent introduction by humans.

Figures

Figure 54. Distribution map of Rhiostoma? Rhiostoma amarapuraense sp. nov. and Rhiostoma sp.

Figure 55. A Rhiostoma? Rhiostoma americana, original figure (after Hanna 1920: pl. 1, fig. 4 a, b) B, C Rhiostoma? Rhiostoma amarapuraense sp. nov. B holotype SMF 130536 / 1 from Amarapura, Burma and C paratype SMF 130536 / 2 - 8 from type locality D-F Rhiostoma sp. D specimens CUMZ 10050 from Khau Nam Nua, Vieng Xai, Houaphanh and E, F specimens CUMZ 10051 from Ban Zox, Xaysetha, Attapeu.