Chersaecia magna (Gude, 1897) Páll-Gergely, Barna, 2018

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 42-44

Chersaecia magna (Gude, 1897) comb. nov.

Figs 5 E–F, 20A–B, 21A–D

Plectopylis magna Gude, 1897 h: 70, fig. 52a–f [“ Burma ”].

Plectopylis lissochlamys Gude, 1897 h: 70–71, fig. 53a–f [“ Burma ”]. Syn. nov.

Plectopylis magna – Gude 1898h: 9–11, fig. 7a–f; 1900b: 91.

Plectopylis lissochlamys – Gude 1898h: 11–13, fig. 8a–f.

Plectopylis (Plectopylis) magna – Gude 1899d: 148; 1899e: 175; 1914b: 122–124, fig. 60a–f. Plectopylis (Plectopylis) lissochlamys – Gude 1899d: 148; 1899e: 175; 1914b: 121–122, fig. 59a–f.

Diagnosis

A medium-sized to large, flat species with two lamellae on the parietal wall, and a main plica free from the apertural fold; palatal wall with typical Plectopylis -like plicae.

Material examined

Types

MYANMAR: 1 shell, holotype of lissochlamys (D = 19 mm), Burma ( NHMUK 1922.8.29.38); 1 shell, holotype of magna (D = 25.4 mm), Burma ( NHMUK 1922.8.29.37).

Additional material

MYANMAR: 1 shell (“ magna ”), Burma, Mergui, coll. Bosch ex Rolle ( SMF 172064); 2 shells (“ lissochlamys ”), Moulmein, coll. Möllendorff ( SMF 150098); 1 shell (“ lissochlamys ”), Burma ( NHMUK 1899.4.22.77); 2 shells (“ magna ”), Tuonghoo, coll. Godwin-Austen ex Blanford ( NHMUK 1923.2.15.5); 2 shells (“ magna ”), Burma, Tonghu, Theobald leg., coll. Blanford ( NHMUK 1906.1.1.731); 1 shell (“ magna ”), Burma ( NHMUK 1899.4.22.78).

LOCALITY UNKNOWN: 2 shells, coll. H.E.J. Biggs, Acc. no. 2258 ( NHMUK).

Description

SHELL. Sinistral, large, thick, pale greyish-yellowish to brown, flat, only protoconch protruding slightly above dorsal surface; protoconch consists of 2.5–2.75 whorls, extremely finely granular and rather regularly, roughly ribbed, rib strength and density increases towards the end of protoconch; suture of protoconch shallow; whorls 7.25–7.5, teleoconch whorls separated by deep suture; teleoconch with rather irregular, dense, fine ribs and only fine striation; body whorl has a much weaker sculpture, ventral side nearly smooth, glossy; body whorl rounded; aperture oval; peristome whitish, expanded and reflected; parietal callus as strongly developed as peristome, rather sharp, slightly S-shaped; apertural fold free from parietal callus, very long, its end visible in oblique view into aperture; umbilicus wide, shallow, funnel-shaped.

The holotypes of Plectopylis magna and P. lissochlamys had been opened. Parietal wall with two lamellae; posterior lamella longer, slender, both ends elongated posteriorly; anterior lamella wider, slightly oblique to shell axis; lower end equally elongated both anteriorly and posteriorly, upper end elongated slightly in posterior direction, with a slightly longer elongation (= short main plica) anteriorly; lower plica slender, reaches peristome. Palatal wall with six main plicae; first situated close to upper suture, long, slightly curved; second plica strongly elongated anteriorly, straight; third short, curved; fourth and fifth join to form a vertical plate; sixth curved, of normal length, situated near lower suture; small denticles visible at posterior ends of all plicae; holotype of P. magna with an additional short horizontal plica between first and second plica.

MEASUREMENTS (in mm). D = 22.1–25.4, H = 7.9–8.9 (holotype of magna , and two other shells); D = 16, H = 6.7 (holotype of lissochlamys ).

Differential diagnosis

Chersaecia leucochila is smaller, has a more elevated spire, a deeper and narrower umbilicus, and its main plica is in contact with the apertural fold. See also under C. feddeni .

Distribution

This species is known from the country of Myanmar only, although the exact type locality is unknown.

Remarks

The holotype of Plectopylis magna differs from that of P. lissochlamys by the larger size, the longer anteriorly elongated lower part of the anterior lamella and the stronger lower plica, which is clearly visible only under the lamellae in P. lissochlamys , but continues only as a slight indication until the peristome in P. magna . All of these characters could be interpreted as intraspecific variability. Therefore, P. lissochlamys is assigned as a synonym of P. magna .

Figures

Fig. 5. Photos (A, C, E) and schematic drawings (B, D, F) of parietal plicae and lamellae of Plectopylinae Möllendorff, 1898. A–B. Chersaecia shanensis (Stoliczka, 1873), loc. 20091018C (PGB, ex coll. Ohara). C–D. Chersaecia perrierae (Gude, 1898), loc. 20091019A (PGB). E–F. Chersaecia magna (Gude, 1897) comb. nov., holotype (NHMUK 1922.8.29.37). Posterior lamella indicated with red colour, anterior lamella and homologous structures indicated with blue. Not to scale. Photos: B. Páll-Gergely (A, C) and H. Taylor (E).