Chersaecia reversalis, Pall-Gergely, 2018

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 24-28

Chersaecia reversalis sp. nov.

urn:lsid:zoobank.org:act:F0E2F58C-B7DD-484E-9B6D-CEFF434FD035

Figs 7 M–N, 8B–C, 11C–D, 13

Diagnosis

Shell small to medium-sized, dextral, parietal wall with a lamella connected to a relatively long intermediate plica, and a long main plica that is free from the lamella and the apertural fold; middle palatal plicae mostly curved, descending posteriorly.

Etymology

The specific epithet refers to the dextral coiling direction, which is unusual in this genus.

Material examined

Holotype

THAILAND: holotype (D = 16.7 mm), Tak Province, Tham Mae Usu (cave), 14 km NNW, 2 km W of Tha Song Yang, 17°17′58″ N, 98°9′52″ E, 200 m a.s.l., 3 May 1988, F.G. Thompson leg. ( UF 347046). Paratypes

THAILAND: 11 shells, same data as for holotype ( UF 448580); 2 specimens (preserved in separate vials of ethanol: PL024 and PL025 used for molecular study), same data as for holotype ( UF 347047); 1 shell, Tak Province, 9.3 km ENE of Ban Huei Hin Fong (ca 19 km ENE of Mae Sot), 15°48′8″ N, 98°41′54″ E, 660 m a.s.l., 26 Apr. 1988, F.G. Thompson leg. ( UF 347296); 3 specimens (preserved in ethanol: adult specimen PL082 used for molecular study; 2 specimens remain intact), same data as for preceding ( UF 347297); 20 shells, Tak Province, 5.5 km NNW of Tha Song Yang, 17°16′13″ N, 98°12′15″ E, 180 m a.s.l., 3 May 1988, F.G. Thompson leg. ( UF 347028); 6 specimens (preserved in ethanol), same data as for preceding ( UF 347029); 3 shells, same data as for preceding ( HNHM 97472); 2 shells, Tak Province, 16 km NNW of Mae Ramat, 17°3′30″ N, 98°26′41″ E, 220 m a.s.l., 3 May 1988, F.G. Thompson leg. ( UF 347425); 3 specimens (preserved in ethanol), same data as for preceding ( UF 347014); 57 shells, Tak Province, 6 km NNW of Tha Song Yang (road 105), loc. 2015/23, 17°15.361′ N, 98°12.654′ E, 140 m a.s.l., 13 Feb. 2015, A. Hunyadi leg. (coll. HA); 2 specimens (preserved in ethanol), same data as for preceding (coll. PGB); 18 shells, Tak Province, 14 + 2 km NNW of Tha Song Yang, around Tham Mae Usu, 17°18.254′ N, 98°09.361′ E, 140 m a.s.l., 15 Feb. 2015, A. Hunyadi leg. (coll. HA); 6 shells, Tak Province, ca 5 km ENE Huai Hin Fon, rock wall above Chao Por Phawo, 16°46.330′ N, 98°41.172′ E, 700 m a.s.l., 16 Feb. 2015, A. Hunyadi leg. (coll. HA); 40 shells, Tak Province, ca 5 km ENE of Ban Huai Hin Fon, rock wall opposing Chao Por Phawo, 16 Feb. 2015, A. Hunyadi leg. (coll. HA); 6 shells, Tak Province, ca 4 km ENE of Ban Huai Hin Fon, 800 m NW of Chao Por Phawo, 16°46.732′ N, 98°40.723′ E, 660 m a.s.l., 16 Feb. 2015, A. Hunyadi leg. (coll. HA); 4 shells, Tak Province, ca 3.5 km ENE of Ban Huai Hin Fon, left side of road no. 12, 16°46.790′ N, 98°39.937′ E, 590 m a.s.l., 16 Feb. 2015, A. Hunyadi leg. (coll. HA); 2 shells, Tak Province, Wat Who Bai Huai Hin Fon, K. Okubo leg. (coll. OKA).

Additional material

THAILAND: 2 juv. specimens (preserved in ethanol), Tak Province, 9.3 km ENE of Ban Huei Hin Fong (ca 19 km ENE of Mae Sot), 15°48′8″ N, 98°41′54″ E, 660 m a.s.l., 26 Apr. 1988, F.G. Thompson leg. ( UF 347297); 2 juv. shells, 1 shell fragment, Tak Province, 5.5 km NNW of Tha Song Yang, 17°16′13″ N, 98°12′15″ E, 180 m a.s.l., 3 May 1988, F.G. Thompson leg. ( UF 347028); 4 juv. shells, Tak Province, 16 km NNW of Mae Ramat, 17°3′30″ N, 98°26′41″ E, 220 m a.s.l., 3 May 1988, F.G. Thompson leg. ( UF 347425); 23 juv. /broken shells, 2 juv. specimens (preserved in ethanol: PL118 and PL119 used for molecular study), Tak Province, 6 km NNW of Tha Song Yang (road 105), 17°15.361′ N, 98°12.654′ E, 140 m a.s.l., 13 Feb. 2015, A. Hunyadi leg. (coll. HA); 18 juvenile /broken shells, Tak Province, 14 + 2 km NNW of Tha Song Yang, around Tham Mae Usu, 17°18.254′ N, 98°09.361′ E, 140 m a.s.l., 15 Feb. 2015, A. Hunyadi leg. (coll. HA); 2 juv. /broken shells, Tak Province, ca 5 km ENE of Ban Huai Hin Fon, rock wall opposing Chao Por Phawo, 16 Feb. 2015, A. Hunyadi leg. (coll. HA).

Description of the type series

SHELL. Dextral, spire slightly elevated, fresh shells have alternating and somewhat variegated reddish and yellowish radial stripes; whorls 6.25–6.5 (n = 5); protoconch finely, irregularly wrinkled with extremely fine granular structure, protoconch whorls separated by a shallow suture, whereas teleoconch whorls separated by deeper sutures; teleoconch sculptured with ribs and spiral striations, giving a reticulated appearance; riblets may have small lamellar periostracal projections within and adjacent to the sutures of each whorl; dorsal surface of whorls with 9–10 spiral lines; spiral striation clearly visible from the beginning of the teleoconch but fading in the final 1–1.5 whorls; reticulated sculpture visible inside umbilicus, periumbilical region smooth, glossy; reticulated upper and smooth lower sculpture change abruptly at middle line of body whorl; peristome white, conspicuously thickened and slightly reflected; parietal callus slightly S-shaped; apertural fold prominent and continuous with main plica.

Five shells were opened. Parietal wall with a short lamella, in contact with intermediate plica; intermediate plica almost twice as long as lamella; main plica long, free from both lamella and apertural fold. Palatal wall with six plicae; first two more or less straight; middle ones oblique, or slightly undulated; posterior end of all middle (second to fifth) plicae descending downwards; last plica slightly curved.

MEASUREMENTS (in mm). D = 18.9, H = 6.5 (holotype); D = 14–16.4, H = 5.9–6.3 (UF 347046, n = 3).

CHARACTERS OF THE GENITAL SYSTEM. One specimen was dissected. Right ommatophoral retractor runs between penis and vagina; penis consists of two portions, a proximal thicker, and a distal slightly longer and slimmer; penis internally with longitudinal, dense, wavy folds; a vestigial penial caecum discernible at junction of penis with epiphallus; retractor muscle very long and inserts on caecum; epiphallus short and tapering to poorly defined junction with the vas deferens, internally with thick, straight longitudinal folds; vas deferens slender; vagina longer, and slightly thinner than penis, connected to body wall with short muscle fibres; vagina internally with slightly wavy longitudinal folds; bursa copulatrix about as long as vagina, with ovoid bursa; diverticulum also originates from base of spermoviduct, shorter and slimmer than bursa copulatrix; inner wall of diverticulum with straight longitudinal folds; 4–5 developing embryos having calcareous crystals on their capsule have been found in uterus.

RADULA. Centrals with small, triangular cusps; endocones of laterals rhomboid; ectocones of first laterals much larger than centrals; ectocones of marginals undivided, endocones of marginals divided by shallow incision.

Differential diagnosis

Chersaecia reversalis sp. nov. differs from Chersaecia dextrorsa by the apertural fold, which is free from the main plica (although in some specimens of dextrorsa these are sometimes connected, see under that species), by the overall weaker sculpture with smooth basal surface, and the mosaic colouration. The anatomy of the two species is strikingly different.

Distribution

The new species is known from several localities in Tak Province, western Thailand ( Fig. 12 ).

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.

Fig. 12. Distribution of plectopylid species in Thailand, Laos and Myanmar. Legends: circle = Chersaecia shanensis (Stoliczka, 1873); filled square = Chersaecia reversalis sp. nov.; empty square = Chersaecia dextrorsa (Benson, 1860); empty rhomb = Hunyadiscus tigrina sp. nov.; filled rhomb = Hunyadiscus saurini Páll-Gergely, 2016; triangle, top up = Plectopylis crassilabris sp. nov.; triangle, top down = Naggsia laomontana (L. Pfeiffer, 1862); empty triangle, top down = Plectopylis bensoni Gude, 1914.