Rhiostoma? amarapuraense Tongkerd & Panha, 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? amarapuraense Tongkerd & Panha sp. nov.

Figs 54 , 55B, C

Type material.

Holotype SMF 130536/1 (Fig. 55B ), collection O. Boettger ex. O. Stoll. Ex. R. Martin. Paratype SMF 130536/2-8 (7 shells; Fig. 55C ), same data as holotype.

Type locality.

Amarapura, Burma [Amarapura Township, Mandalay District, Mandalay Region, Myanmar].

Diagnosis.

Shell small, thin, and depressed; detached whorl shorter than apertural width. Shell colour with brownish zigzag pattern, without peripheral band. Breathing device with short tubular shape.

Differential diagnosis.

Rhiostoma ? Rhiostoma amarapuraense sp. nov. can be distinguished from R. strubelli by having a depressed shell, outer lip expanded, without a peripheral band, and with a short tubular-shaped breathing device. In contrast, R. strubelli from Shan State, Myanmar, displays an elevated spire, with a dark brown peripheral band, thickened multi-layered apertural lip, and breathing device as a short and incomplete tube.

Description.

Shell. Shell small, width 20.0-21.5 mm, height 10.0-10.1 mm, thin, and nearly flattened shape. Apex acute and with dark colouration; spire slightly elevated. Whorls 4 to 5, convex, increasing regularly; suture wide and shallow; last whorl rounded. Shell surface with fine growth lines. Periostracum thin, corneous, and transparent. Shell with brown zigzag pattern, without peripheral band. Detached whorl shorter than apertural width. Peristome circular and double; lip slightly thickened and expanded. Aperture opened sub-laterally. Breathing device with short tubular shape; outer lip protruding, with short closed tube and expanded; inner lip with small hole inside aperture. Umbilicus widely opened and deep. Operculum unknown (Fig. 55B, C ).

Etymology.

The species name amarapuraense refers to the collection locality of this new species. In addition, Amarapura is a former capital of Myanmar during the late 18th to early 19th century, but now is a township in Mandalay District, Mandalay Region.

Distribution.

This new species is currently known only from the type locality (Fig. 54 ).

Remarks.

This specimen lot SMF 130536 was originally identified as " Pterocyclos cf. pullatus Bens." and was described from Akaouktong, near the Ayeyarwady River, Myanmar. This new species differs from Pterocyclos pullatus Benson, 1856 in having a depressed shell, short detached whorl, tubular-shaped breathing device, outer lip protruding, with a closed tube, inner lip with a small hole inside the aperture, apertural lip expanded, and widely opened umbilicus. For comparison, the syntype of " Pterocyclos pullatus " has a helicoid shell, without detached whorl, breathing device notch-shaped, outer lip protruding, with wide groove, inner lip with wide and deep incision, apertural lip blunt (slightly thickened but not expanded), and umbilicus narrow and deep ( Preece et al. 2022: fig. 29c).

Although R. ? Rhiostoma amarapuraense sp. nov. is nominated based solely on shell morphology without its operculum, all the type series have the unique characters of the Rhiostoma , including the peristomal breathing device and the detached whorl. However, the generic placement is still provisional and awaits further collection of living specimens with operculum to confirm generic placement. This species is clearly distinct from other known Rhiostoma and Pterocyclos species from eastern India and Myanmar.

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.