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 21 N–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. 21. Parietal (A, C, E, G, I, J, L, N, P, R) and palatal (B, D, F, H, K, M, O, Q, S) plication of species of Chersaecia Gude, 1899. A–B. C. magna (Gude, 1897) comb. nov., holotype (NHMUK 1922.8.29.37). C–D. C. magna (“P. lissochlamys”, after Gude 1914b). E–F. C. mogokensis sp. nov., holotype (NHMUK 20140787). G–H. C. nagaensis (Godwin-Austen, 1875), syntypes (NHMUK 1903.7.1.753). I. C. nagaensis (NHMUK 1874.9.26.3). J–K. C. nagaensis muspratti (Gude, 1897) (after Gude 1914b). L–M. C. perarcta simplex (Solem, 1966) (after Solem 1966). N–O. C. perarcta perarcta (Blanford, 1865) (NHMUK 1906.2.2.275). P–Q. C. perarcta perarcta (UF 448575). R–S. C. perarcta perarcta, loc. “5.5 km west of Chiang Rai” (coll. PGB). Arrows below the letters indicate the direction of the aperture. Not to scale.

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.