Chersaecia perrierae
Creators: name: Páll-Gergely, Barna
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Plectopylidae
Chersaecia
Chersaecia perrierae

description: Chersaecia perrierae (Gude, 1898)
Figs 5 C–D, 16C–D, 23A–B, 24A–B, 25
Plectopylis perrierae Gude, 1898a: 231–232, fig. 67a–f [“Thayet-Mayo, Pegu, Burma ”].
Plectopylis perrierae – Gude 1898h: 14–16, fig. 10a–f.
Plectopylis (Chersaecia) perrierae – Gude 1899d: 148; 1899e: 175; 1914b: 103–105, fig. 48a–f. Chersaecia perrierae – Páll-Gergely et al. 2015c: 10.
Diagnosis
A small, sinistral, flat species with a single lamella and rarely a second, vestigial, anterior lamella, long main, lower, and intermediate plicae on the parietal wall, and Plectopylis -like plication on the palatal wall.
Material examined
Holotype MYANMAR: 1 shell (D = 14.8 mm), Pegu [Bago], ex coll. Linter (NHMUK 1922.8.29.40).
Additional material
MYANMAR: 2 shells, Burmah, Kyengdwen Valley, Ogle leg., coll. Godwin-Austen (NHMUK 1903.7.1.776); 4 shells, Fort Stedman, coll. Godwin-Austen (NHMUK); 74 shells, Shan, Pindaya, Pindaya Cave, loc. 20091019A, 20°55.409′ N, 96°39.038′ E, 1294 m a.s.l., 19 Oct. 2009, K. Ohara, K. Okubo and J.U. Otani leg. (coll. OK); 5 shells, same data as for preceding (coll. PGB, ex coll. K. Ohara); 1 shell, same data as for preceding (coll. PGB, ex coll. J.U. Otani); 1 shell + ethanol-preserved body (anatomically examined), same data as for preceding (NHMUK 20170148).
Description
The holotype (NHMUK 1922.8.29.40) and two additional shells from the Kyengdwen Valley (NHMUK 1903.7.1.776) are from different samples, yet they differ only in size; therefore, the shell description is based on these three specimens. The differences between those three shells and the specimens collected from locality 20091019 A are mentioned in the Remarks.
SHELL. Sinistral, almost entirely flat, only protoconch protrudes above dorsal surface; all three specimens were corroded, therefore original colour could not be observed; protoconch consists of 2.75–3 whorls, finely tuberculated, last whorl irregularly, roughly wrinkled; teleoconch finely reticulated on dorsal side, elsewhere ribs dominant (holotype reticulated on entire surface); whorls 6–6.5 (n = 3), separated by a rather shallow (holotype) or moderately deep (other two shells) suture; body whorl rounded but angulated above (dorsal side flat); peristome slightly thickened and very slightly reflected; parietal callus elevated, sharp, V-shaped, upper (from standard apertural view) branch of V being shorter.
Two opened shells were examined (= holotype and one shell from the other sample). Parietal wall with a single, strong, curved lamella with posteriorly elongated lower end; main plica long, free from lamella, curved downwards (its posterior end situated above middle point of lamella, then runs a bit lower anteriorly, reaching middle line of lamella, and runs upwards again); lower plica very slender, starts under lamella and reaches peristome, but interrupted in its middle. Palatal plicae six; first, second and third straight and horizontal or slightly oblique; fourth and fifth form a vertical plate with a bifurcated lower end; sixth very long and divided, its anterior part much longer than the posterior.
MEASUREMENTS (in mm). D = 14.8, H = 5.9 (holotype); D = 12.6–12.9, H = 4.5–4.7 (NHMUK 1903.7.1.776, n = 2); D = 11.1–11.95, H = 3.8–5.2 (20091019 A, n = 3).
CHARACTERS OF THE GENITAL STRUCTURE. One specimen was anatomically examined (NHMUK 20170148). Left ommatophoral retractor passes between penis and vagina; atrium very short; penis long, slender, cylindrical; internally with longitudinal folds; epiphallic differentiation not observed; vas deferens originates from penial wall approximately at middle of penis; retractor muscle inserts on proximal end of penis, as thick as penis and slightly shorter; vas deferens derives from penial section; between middle penial section and reflected part of vagina vas deferens slender, and runs together with vagina, attached to it with weak fibres; from reflected part of vagina vas deferens gradually thickens, even exceeds diameter of penis, and becomes free from vagina (i.e., not attached to it by fibres); vagina cylindrical, slightly flattened close to atrium, internally with longitudinal folds; slightly longer than penis, and about 2–3 times thicker; several slender muscle fibres attach vagina to body wall; pedunculus short, spermoviduct strongly developed, uterus with four large embryos; bursa copulatrix approx. 2 times longer than diverticulum; diverticulum relatively thick, internally with parallel longitudinal folds; bursa slightly thickened (reaching diameter of diverticulum); both organs originate near the point where vas deferens joins pedunculus.
RADULA. Centrals with very small, triangular cusps; endocones of laterals rhomboid or slender ovoid with pointed tips; ectocones of first laterals much larger than centrals; ectocones of marginals undivided, endocones of marginals divided by shallow incision.
Differential diagnosis
Chersaecia perrierae differs from C. leiophis by the brownish shell, long lower plica which reaches the peristome (this is very short in leiophis) and the main plica, which is straight in C. leiophis, but curved downwards in C. perrierae.
The angled body whorl resembles that of the nearby occurring Chersaecia woodthorpei. However, that species has two distinct lamellae and three short, parallel, straight palatal plicae next to the vertical plate which is formed by the fourth and fifth plicae.
Distribution
This species is known from a few localities in Myanmar. The most recent sample was collected from the eastern part of the Shan Region.
Remarks
The newly collected sample from Myanmar (20091019 A) provides additional information to the old museum specimens in terms of shell colour and sculpture. The shell colour is reddish brown, and the protoconch is finely tuberculated. The shells belonging to this sample are overall smaller and flatter than the others described above and have more angulated body whorls. The main plica strongly curves down in the direction of the intermediate plica. The area between the two plicae may be covered with a white calcareous layer, which is probably homologous with the anterior lamella of other species of Chersaecia and Plectopylis (Fig. 5).
description: Published as part of Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), pp. 1-114 in European Journal of Taxonomy 455 on pages 52-56, DOI: 10.5852/ejt.2018.455, http://zenodo.org/record/3817707