Plectopylis thompsoni, Pall-Gergely, 2018

Páll-Gergely, Barna, 2018, Systematic revision of the Plectopylinae (Gastropoda, Pulmonata, Plectopylidae), European Journal of Taxonomy 455, pp. 1-114 : 102-103

Plectopylis thompsoni sp. nov.

urn:lsid:zoobank.org:act:21175C88-45BD-4DFE-9EAD-A16FCB9B623E

Figs 35 N–O, 44F, 46C–D, 47

Diagnosis

A large, sinistral, flat species with a strongly developed lip and a long apertural fold that is in contact with the peristome; right leg of lambda-complex absent.

Etymology

The new species is dedicated to and named after Fred Gilbert Thompson (1934–2016), who collected most of the material examined for this publication.

Material examined

Holotype

THAILAND: 1 shell (D = 23 mm), Trang Province, limestone mountain, 7 km S/ 2 km E of Huai Yot , 7°44′N 99°38′E, 40 m a.s.l., 28 Sep. 1985, F.G. Thompson leg. ( UF 77249 ).

Paratypes

THAILAND: 14 shells, same data as for holotype ( UF 448578); 13 specimens (preserved in ethanol: PL069 and PL070 used for molecular study), same data as for holotype ( UF 76482); 2 shells, same data as for holotype ( HNHM 97463); 1 shell, Krabi Province, 10 km NE of Ao Luk, 8°29′ N, 98°49′ E, 30 Sep. 1985, F.G. Thompson leg. (mixed sample with P. cairnsi ) ( UF 507377); 1 shell, same data as for preceding ( HNHM 97476); 17 shells, Trang Province, limestone mountain, 7 km S/ 2 km E of Huai Yot, 40 m a.s.l., 28 Sep. 1985, F.G. Thompson leg. ( UF 77250); 2 shells, same data as for preceding ( HNHM 97477).

Description

SHELL. Sinistral, flat, fresh shells with yellowish- and reddish-corneous markings resembling tigerstripes, or with a mosaic-like pattern; protoconch consists of 3.25–3.5 whorls, very fine granulose with fine growth wrinkles near suture; last whorl of protoconch irregularly, finely ribbed; teleoconch with irregular growth lines and rather regular spiral striation; entire shell consists of 5.25–6 whorls; aperture oval; peristome conspicuously thickened and slightly reflected; parietal callus also thickened; apertural fold in contact with parietal callus.

Six shells were opened. Lambda-complex incomplete (right leg absent); upper branch strongly elongated posteriorly; main plica connected to lambda-complex, starts from just below meeting point of left leg and upper branch; a short lower plica also present below main plica; lower plica usually free but can be in contact with left leg. Palatal wall typical of Plectopylis .

MEASUREMENTS (in mm). D = 18.3–23.3, H = 6.3–7.4 (n = 4).

CHARACTERS OF THE GENITAL SYSTEM. Two specimens of sample UF 76482 were examined ( Fig. 47 ). One of the specimens was aphallic (PL069), its male genitalia consisted of a small wart-like structure, which was connected to the vas deferens. The female parts of that specimen appeared normal. Moreover, a spermatophore (long, fragile, reddish brown tube-like thread folded multiple times and forming an ovate mass with pointed ends) was found in the diverticulum. The description of the traits of the genital structure of the other specimen are as follows: left ommatophoral retractor runs between penis and vagina; penis relatively long, with slender distal, and thickened proximal part, internally with parallel, serrate folds; epiphallus and vas deferens attached to penis with weak muscle fibres; no penial caecum observed; retractor muscle thick, slightly shorter than penis, inserts on proximal part of penis; vagina slightly shorter than penis, but thicker; bursa copulatrix with a very long, slender stalk, bursa strongly elongate ovoid, only slightly thickened; diverticulum small, oval; three developing embryos found in uterus, covered by fine calcareous powder-like crystals.

RADULA. Centrals nearly entirely reduced; endocones of laterals rhomboid or elongate-ovoid with pointed tip; ectocones of marginals undivided; endocones of marginals mostly undivided, or divided by shallow incision.

Differential diagnosis

Plectopylis thompsoni sp. nov. can be distinguished from all other species of Plectopylis by the reduced right leg of the lambda-complex. In shape, P. thompsoni sp. nov. resembles P. anguina , but that species is larger, its aperture is more oblique to the shell axis, has a bluntly keeled body whorl and lacks the spiral lines, which are prominent in P. thompsoni sp. nov. Plectopylis thompsoni sp. nov. is larger than P. malayana sp. nov. and its apertural fold reaches the parietal callus. Plectopylis cairnsi , which also occurs sympatrically with P. thompsoni sp. nov., is usually smaller than the new species, has a thinner apertural fold and peristome, a less descending aperture, and usually has a more elevated spire. Shells of P. bensoni of the same diameter as P. thompsoni sp. nov. are higher, their protoconch protrudes above the dorsal surface and they lack spiral lines on the body whorl.

Distribution

Two localities are known from the limestone hills of northern Trang Province. One additional shell was found in a sample of Plectopylis cairnsi from northern Krabi Province. I cannot rule out the possibility that the shell of P. thompsoni sp. nov. was mistakenly included in that sample. Therefore, the presence of this new species in Krabi Province needs confirmation ( Fig. 40 ).

Figures

Fig. 35. Parietal (A–E, G, I–L, N) and palatal (F, H, M, O) plication of species of Plectopylis Benson, 1860. A. P. anguina Gould, 1847, paralectotype (NHMUK 20140812). B. P. repercussa Gould, 1856, lectotype (MCZ 169336). C. P. bensoni var. repercussoides Gude, 1899, holotype (NHMUK 1922.8.29.46). D. P. cairnsi Gude, 1898, holotype (NHMUK 1922.8.29.47). E–F. P. cairnsi (UF 76761). G–H. P. crassilabris sp. nov., paratype (UF 448577). I. P. cyclaspis Benson, 1859 (NHMUK 1906.02.02.148). J. P. karenorum (W. Blanford, 1865) from “Pegu”, Myanmar (NHMUK). K. P. linterae var. fusca Gude, 1898 (NHMUK 1888.12.04.1541–3). L–M. P. malayana sp. nov., paratypes from the type locality (coll PGB). N–O. P. thompsoni sp. nov., paratype (UF 448578). Arrows below the letters indicate the direction of the aperture. Not to scale.

Fig. 47. Genitalia of Plectopylis thompsoni sp. nov. A. Distal genitalia, PL070 (UF 76482). B. Genitalia of an aphallic specimen, PL069 (UF 76482). C–D, F–G. Inner structure of genital organs (C = penis, D = epiphallus, F = vagina, G = diverticulum), PL070 (UF 76482). E. Spermatophore, PL070 (UF 76482). Scale bars: A–B = 5 mm; C–G = 1 mm. For abbreviations see Fig. 2. All photos: B. Páll-Gergely.

Fig. 40. Distribution of species of Plectopylis Benson, 1860 in Southern Thailand and northern Malaysia. Legends: empty triangle = P. thompsoni sp. nov.; square = P. cairnsi Gude, 1898; filled triangle = sympatric locality of P. thompsoni sp. nov. and P. cairnsi; circle = P. malayana sp. nov.