Chersaecia perarcta perarcta ( Blanford, 1865 )

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 50-51

Chersaecia perarcta perarcta ( Blanford, 1865)

Figs 21N–S, 22C–D

Helix (Plectopylis) perarcta Blanford, 1865: 75 , 94 [“Mya Leit Doung, near Ava”].

Helix perarcta – Pfeiffer 1868: 397–398; 1869: 502, pl. 108, figs 13–15.

Helix (Plectopylis) perarcta – Hanley & Theobald 1870: 7, pl. 13, fig. 3. — Godwin-Austen 1875b: 613, pl. 74, fig. 4. — Nevill 1878: 71. — Tryon 1887: 162, pl. 35, figs 91–95. — Godwin-Austen 1888: 243 [“Hlindet, 1200 feet ”].

Plectopylis perarcta – Gude 1896a: 155, fig. 19a–c; 1908: 88.

Plectopylis (Chersaecia) perarcta – Gude 1899d: 148; 1899e: 175; 1914b: 106–108, fig. 50a–c.

Chersaecia perarcta – Páll-Gergely et al. 2015c: 10.

Diagnosis

Main plica present.

Material examined

Types

MYANMAR: 6 shells (probably syntypes), Burma, Myaleit doung, Ava, ( NHMUK 1906.2.2.275); 3 shells (probably syntypes), Myaleit doung, near Ava ( NHMUK 1888.12.4.1521–1523).

Additional material

MYANMAR: 3 shells, Burma, coll. Godwin-Austen ex Blanford ( NHMUK 1909.3.15.61); 1 shell, Burma, Ava, coll. A. S. Kennard ( NHMUK); 3 shells, Burma, Ava ( NHMUK).

THAILAND: 1 shell, Chiang Rae Province, limestone knoll, 4 km NE of Ban Pa Ngae, 19°34′19″ N, 99°59′14″ E, 410 a.s.l. m, 12 May 1988, F.G. Thompson leg. ( UF 380334); 20 shells, 3 juv. shells, same data as for preceding ( UF 448575); 2 shells, same data as for preceding ( HNHM 97459); 8 shells, 6 juv. shells, same data as for preceding but 13 May 1988 ( UF 380344); 1 shell, Wat Phra That Tham Doi Kong Kao, ca 5.5 km W of Chiang Rai, in clay in Temple Cave, 19°54′46.34″ N, 99°46′33.64″ E, Sep. 2007, A. Reischütz leg. ( HNHM 97458); 2 shells, 2 damaged shells, same data as for preceding (coll. PGB); 2 shells, same data as for preceding ( NHMW 108116); 24 shells, 10 damaged shells, same data as for preceding (coll. REI).

Description of the type series

SHELL. Sinistral, tightly coiled, flat, only protoconch protrudes above dorsal surface; colour greyish yellow to light brown; protoconch large, consists of 2.5–2.75 whorls, with large tubercles, no radial lines visible; teleoconch with very fine ribs, covered by fine periostracal folds; spiral lines absent; periostracum more prominent inside sutures; whorls 5.75–6, separated by very deep suture; umbilicus regularly shaped infundibular, only last whorl widening abruptly; body whorl rounded; peristome reflected and slightly thickened; parietal callus elevated, sharp, V-shaped.

Two shells were opened. Parietal wall with a single, strongly developed lamella, which has the lower end elongated slightly posteriorly; upper end very slightly elongated in both anterior and posterior directions; main plica long, free from lamella, reaches parietal callus; one of the shells had the main plica and the apertural fold separated (probably subadult shell); inner end of main plica situated lower (closer to the lower suture); lower plica slender, runs along and parallel with lower suture and also reaches parietal callus; there is a very short additional plica between the main and lower plica; all plica start in one vertical line anterior to lamella. Palatal plicae six; first and sixth straight, run parallel with sutures; middle plicae more or less horizontal, straight or slightly wavy; sometimes with additional posterior denticle.

MEASUREMENTS (in mm). D = 10.9–12.8, H = 4–4.5 (UF 38344, n = 5); D = 11.2–13, H = 3.7–4.5 (loc. “ 5.5 km west of Chiang Rai ”, coll. REI); D = 10.6–11.7, H = 3.6–4.1 (type series, NHMUK 275.06.2.2, n = 3).

Differential diagnosis

See under Chersaecia perarcta simplex .

Distribution

Chersaecia perarcta perarcta has been reported from the vicinity of Ava, Mandalay Region, Myanmar, and from northern Thailand (see also Fig. 17 ).

Remarks

Typical shells have a well-developed apertural fold, which is in contact with the parietal callus. The apertural fold of the shells collected 4 km NE of Ban Pa Ngae is free from the parietal callus. Most of the shells (23 out of 27) from 5.5 km W of Chiang Rai lacked the apertural fold, and all four opened shells lacked a lower plica.

Figures

Fig. 17. Distribution of plectopylid species in Northern Thailand. Legends: circle = Chersaecia auffenbergi sp. nov.; triangle = Chersaecia leiophis (Benson, 1860) (empty triangle shows the type locality of Plectopylis degerbolae Solem, 1966); empty square = Chersaecia perarcta simplex (Solem, 1966); cross = Chersaecia perarcta perarcta (Blanford, 1865); filled square = Chersaecia scabra sp. nov.; rhomb = Chersaecia densegyrata sp. nov.; the upper filled triangle also shows the locality of Naggsia oligogyra sp. nov.