Chersaecia densegyrata, Pall-Gergely, 2018

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 18-20

Chersaecia densegyrata sp. nov.

urn:lsid:zoobank.org:act:9468E60C-F711-46B3-8BD5-E7983BC2E36F

Figs 7 C–D, 8A

Diagnosis

A small, dextral, flat species with 6.5 slowly increasing whorls. Parietal wall with a single lamella, main plica free from lamella and apertural fold; intermediate plica attached to lower end of lamella. On the palatal wall there are two vertical plicae, with one horizontal plica below and three above.

Etymology

The name “ densegyrata ” refers to the rapidly increasing whorls of the new species.

Material examined

Holotype

THAILAND: 1 shell, Chiang Mae Province , 20 km SSW of Ban Mae Khi, 19°34′40″ N, 99°4′52″ E, 700 m a.s.l., 22 Jun. 1987, F.G. Thompson leg. ( UF 347223).

Description

SHELL. Dextral, white and light-brown striped; concave above, only protoconch protrudes above dorsal surface; protoconch consists of 2.5 whorls, first ca 1.5 whorls almost smooth with very small tubercles, remaining ones irregularly ribbed; entire shell with 6.5 whorls, slowly increasing, separated by rather deep suture, but dorsal surface of whorls flat; teleoconch finely decussated with low riblets and spiral lines; aperture relatively small; peristome strongly thickened and slightly reflected; parietal callus elevated, sharp, in contact with apertural fold, which is free from main plica; periumbilical area (ventral shell side around funnel-shaped umbilicus) nearly smooth.

Parietal wall with short vertical lamella, and intermediate plica, connected to lower end of lamella; main plica long, free from lamella and apertural fold. Palatal wall with six plicae, with second being longest; first, second, third and last plicae straight and horizontal; fourth and fifth vertical.

MEASUREMENTS (in mm). D = 13.5, H = 5 (holotype).

Differential diagnosis

Chersaecia densegyrata sp. nov. is similar to C. dextrorsa and C. reversalis sp. nov. in terms of coiling direction, but it is smaller and much flatter than the latter two species, and has rapidly-increasing whorls. There are also differences in the plication: the intermediate plica of C. dextrorsa and C. reversalis sp. nov. extends beyond the lamella in posterior direction, whereas it stops when reaching the lamella in the new species. Furthermore, the fourth and fifth palatal plicae of C. densegyrata sp. nov. are vertical.

Distribution

The new species is known from the type locality only.

Figures

Fig. 7. Parietal (A, C, E, G, J, K, M) and palatal (B, D, F, H, I, L, N) plication in species of Chersaecia Gude, 1899. A–B. C. austeni (Gude, 1899) (1903.06.01.1014.1). C–D. C. densegyrata sp. nov. (UF 347223). E–F. C. dextrorsa (Benson, 1860) (UF 346181). G–H. Chersaecia dextrorsa (UF 76507). I–J. C. brachyplecta (Benson, 1863) comb. nov. (after Gude 1914b). K–L. C. smithiana (Gude, 1897) comb. nov. (NHMUK 1888.12.4.1555–1556, two different specimens). M–N. C. reversalis sp. nov., paratype from type locality (UF 347046). Arrows below the letters indicate the direction of the aperture. Not to scale.