Plectopylis anguina

Plectopylis anguina (Gould, 1847)

Figs 34A, 35A

Helix anguina Gould, 1847: 218–219 [“Manko, near Newville, Province of Tavoy”].

Helix (Plectopylis) anguina – Hanley & Theobald 1870: 7, pl. 13, fig. 7. — Godwin-Austen 1875b: 613. — Nevill 1878: 72. — Tryon 1887: 165, pl. 35, fig. 6.

Plectopylis anguina – Gude 1898d: 76, fig. 79a–f (on page 75).

Plectopylis (Plectopylis) anguina – Gude 1899d: 148; 1899e: 175; 1914b: 136–138, fig. 69a–f. — Johnson 1964: 40, pl. 41, fig. 5. (fig. caption before pl. 38, shell photo mixed up with Cyclostoma (Cyclophorus) cucullata).

Diagnosis

A very large, sinistral species with conspicuously flattened shell, and bluntly keeled body whorl.

Material examined

Types MYANMAR: 2 shells, paralectotypes, Tavoy (NHMUK 20140812); 1 shell, paralectotype, Manko, Tavoy, coll. Gould (MCZ 147595); 1 shell, lectotype, Burmah, Manko, near Newville, Tavoy, Mrs Vinton leg., coll. Gould (MCZ 169042); 1 shell, paralectotype, same data as for preceding (MCZ 169043).

I examined the paralectotypes in the NHM, and received photographs of specimens deposited in the MCZ.

Additional material

MYANMAR: 1 shell, Burmah, Moulmein, 1908, coll. C.R. Boettger (SMF 102815); 1 shell (mixed sample with Plectopylis bensoni) (SMF 172059); 1 shell, Burma, coll. Bosch ex Rolle (SMF 345109); 3 shells, Mergui (NHMUK); 1 shell, Rangoon, Moulmein, coll.Godwin-Austen (NHMUK 1903.7.1.739); 1 shell, Rangoon, Moulmein, coll. Blanford (NHMUK 1906.1.1.732); 1 shell, Molmein (NHMUK); 2 shells, Damathat Hill (NHMUK 1888.12.4.1553–1554).

Description of the type series

SHELL. Sinistral, strongly depressed, dorsal surface slightly concave, but protoconch protrudes to reach level of dorsal surface; whorls 5–5.75 (n = 2); body whorl bluntly keeled; whole shell brownish with yellowish stripes, dorsal side seems to be darker than ventral; one specimen was almost completely brown above and striped below, whereas other shells were striped above and almost completely pale on their ventral side; protoconch matt, almost smooth, with irregular, inconspicuous growth lines and extremely small granular structure; teleoconch dominated by irregular growth lines, and some reticulated parts on dorsal surface (between end of protoconch and beginning of last whorl); periphery of body whorl almost smooth; aperture almost completely facing downwards; peristome strongly thickened and slightly reflected; parietal callus quite low, slightly depressed V-shaped; apertural fold starts at some distance from parietal callus.

One opened shell was examined. Lambda-complex complete; both legs with slight elongations anteriorly and posteriorly; upper branch slightly longer than elongation of left leg; main plica connected to the right leg. Palatal plicae typical of Plectopylis.

MEASUREMENTS (in mm). D = 26.2–30.4, H = 7.1–7.9 (paralectotypes, NHMUK 20140812, n = 2).

Differential diagnosis

Plectopylis anguina differs from P. bensoni by the lighter, flatter shell, the bluntly keeled body whorl, the more elongated aperture and the overall more elongated (ovate) shell outline.

Distribution

The species has been reported from a few southern Burmese localities.

Remarks

Gude (1914b) mentioned that Plectopylis anguina differs from P. repercussa in features of the parietal plication. Namely, “the lower arm of the bifurcation” is longer than the upper, whereas the reverse is true in P. repercussa. In the opened paralectotype in the NHM this was not the case, because the upper arm was very slightly longer then the lower leg. The other difference mentioned by Gude is that the lower plica does not extend beyond the left leg in P. anguina, but does so in P. repercussa. My observations do not match those of Gude, because the lower plica does not exceed the left leg in the opened paralectotype of P. repercussa. Therefore, this character does not distinguish the two species. Based on this evidence, P. anguina is a valid species, different from P. bensoni (of which P. repercussa is a synonym) because of its characteristic flat shell, strongly oblique aperture and bluntly keeled body whorl.