Chersaecia refuga ( Gould, 1846 )

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 57-58

Chersaecia refuga ( Gould, 1846)

Figs 23 C–E, 24C–D

Helix refuga Gould, 1846: 99 [“Tavoy”].

Helix refuga – Philippi 1847: 52 (=2), pl. 10, fig. 4 [“imperium Birmanorum Indiae orientalis”]. —

Pfeiffer 1848a: 383–384, pl. 66, figs 21–23. — Reeve 1854: species 436, pl. 82, fig. 436a–b. —

Theobald 1857: 249. — Pfeiffer 1868: 396. Helix (Atopa) refuga – Albers 1850: 90. Helix (Corilla) refugum – Adams H. & Adams A.1855: 208. Helix (Corilla) refuga – Gould 1862: 198. Helix (Plectopylis) refuga – Nevill 1878: 71. — Tryon 1887: 164, pl. 35, fig. 1. Plectopylis refuga – Gude 1898c: 15–16, fig. 75a–e. Plectopylis (Chersaecia) refuga – Gude 1899d: 148; 1899d: 148; 1899e: 175; 1914b: 102–103,

fig. 47a–e. Plectopylis (Plectopylis) refuga – Johnson 1964: 139, pl. 38, fig. 9. Chersaecia refuga – Páll-Gergely et al. 2015c: 10.

Diagnosis

Shell medium-sized, widely umbilicated, flat, periumbilical region glossy; parietal wall with a single lamella, short middle and main plicae; palatal wall with 6 parallel plicae.

Material examined

Types

MYANMAR: 1 shell, lectotype (D = 17.8 mm), Tavoy, British Burma ( MCZ 169335); 1 shell, paralectotype of refuga (photos examined), Tavoy, Burma, coll. Gould ( MCZ 87871).

Additional material

MYANMAR: 1 shell (mixed sample with C. leiophis : NHMUK 20150360), Burma, ex Museum Cuming ( NHMUK 20170160); 1 shell (mixed sample with C. leiophis : NHMUK 20170161), India, Thyet Myo ( NHMUK 20170162).

Description

SHELL. Sinistral, entirely flat; colour off-white to pale yellowish-grey, surface overall glossy; protoconch consists of 2.5–2.75 whorls, rather glossy with very fine granular surface and irregular wrinkles; ventral part of body whorl (periumbilical region) smooth, glossy; dorsal surface and area inside umbilicus dominated by spiral striation, or spiral and radial lines of the same strength; periphery of body whorl dominated by radial lines; whorls 6–6.25, separated by comparatively shallow suture; whorls angled; aperture rounded; peristome expanded and slightly reflected; parietal callus elevated, rather sharp and V-shaped; apertural fold connected to parietal callus.

Two opened shells were examined. Parietal wall with a single curved lamella; middle and intermediate plicae short, free from lamella; lower plica absent. Palatal wall with six plicae, first short, with an additional denticle at its posterior end; second longer (but shorter than in other species of the genus), posterior end curved downwards; third short, also curved; fourth and fifth form a vertical plate, with small connecting denticles posteriorly; sixth very short.

MEASUREMENTS (in mm). D = 15.9–17.8, H = 6.6–7.4 (n = 3, lectotype + specimens from the NHM).

Differential diagnosis

Chersaecia refuga has been confused with C. leiophis . The two species are similar, but can be easily distinguished based on the following differences: (1) refuga is entirely flat and its whorls are more strongly shouldered (both above and below) than those of C. leiophis ; (2) the umbilicus of C. refuga is wider and more regularly funnel-shaped; (3) the periumbilical region, which is sharper than that of C. leiophis , is glossy (reticulated in C. leiophis ); (4) the plicae anterior to the lamella are shorter than in C. leiophis ; (5) the palatal plicae are shorter; (6) the protoconch and the entire shell is glossier than that of C. leiophis .

Distribution

All known shells have been collected in southern Myanmar.

Remarks

Chersaecia refuga has been confused with C. leiophis by previous authors. Godwin-Austen (1875a) claimed that the two species are identical, based on the examination of Cuming’s shells, which were labelled as Plectopylis refuga . According to Gude (1914b), the same shells, which were examined by Godwin-Austen and figured by Philippi (1847), Pfeiffer (1848a) and Reeve (1854) (now NHMUK 20150360), are in fact C. leiophis . However, since Gude could not examine the type specimens of P. refuga , he was unable to recognise that the sample of Cuming contained both species. It is difficult to tell which species was figured in the mentioned literature, but the light coloured periumbilical region and the wide umbilicus characteristic for C. refuga suggests that they were showing C. refuga instead of C. leiophis .

Gude (1898c) was unable to borrow the type specimen of Plectopylis refuga , and received only drawings and photos from the curator of the New York State Museum. Dr. Merrill’s drawings show one or two shells, which were opened to show the parietal plicae and lamellae. I borrowed the lectotype of P. refuga (MCZ 169335) and examined photos of two samples of paralectotypes (MCZ 87871, 142866). The sample MCZ 87871 contained a single shell which is very similar to the lectotype of P. refuga . The other sample (MCZ 142866) contained five shells, which probably belong to a different species (possibly Chersaecia feddeni ) because they have rounded body whorls, which are shouldered in C. refuga . Both the lectotype (MCZ 169335) and the similar paralectotype (MCZ 87871) have a small hole on the shell ca halfway between the armature and the aperture. This hole, however, does not allow for careful examination of the parietal lamella and the adjacent plicae. Thus, it is unclear which shells were examined and figured by Dr. Merrill. Two opened shells of C. refuga were found in the NHM, which allowed the examination of the parietal plication.

Figures

Fig. 23. Shells and protoconch of species of Chersaecia Gude, 1899. A. C. perrierae (Gude, 1898), holotype (NHMUK 1922.8.29.40). B. C. perrierae, loc. 20091019A, Specimen 2 (coll. PGB). C–E. C. refuga (Gould, 1846), lectotype (MCZ 169335). Scale bar: A–C = 10 mm. Images: B. Páll-Gergely (B–E) and H. Taylor (A).