Plekocheilus (Plekocheilus) vlceki, Breure, Abraham S. H. & Schlögl, Jan, 2010

Breure, Abraham S. H. & Schlögl, Jan, 2010, Additional notes on Orthalicidae from the Chimantá massif, Venezuelan Guayana, with descriptions of new species of Plekocheilus Guilding, 1828 (Mollusca: Gastropoda), Zootaxa 2416, pp. 51-60 : 52-54

Plekocheilus (Plekocheilus) vlceki spec. nov.

( Figs 2 A–2C, 3A, 3B, 4A)

Diagnosis. A small species of Plekocheilus s. str. (up to 30.9 mm) that is characterized by its almost uniform (dark-) yellowish to chestnut-brown colour, its finely malleated sculpture on the last whorl crossed by spiral lines and a rather strong columellar fold.

Description. Shell: Up to 30.9 mm high, 1.75 times longer than wide, imperforate, ovate, sides of spire slightly convex, moderately solid. Colour yellowish- to dark chestnut-brown; upper whorls lighter, whitish, eroded. Surface somewhat shining, with closely set riblets on the upper whorls, becoming finely malleated on the last whorl, crossed by spiral lines. Protoconch smooth (eroded). Whorls 4.0, rather flat, the last whorl slightly swollen; suture impressed, somewhat descending in front. Aperture elongate-ovate, somewhat pointed above, the stripes or spots from the outside shining through, in some specimens whitish inside, 1.6 times longer than wide, 0.51 times the total length; peristome thickened and strongly reflexed, dark brown. Columellar margin slightly curved, with a rather strong fold above, hardly and narrowly dilated above. Parietal wall with a thin, brownish callus.

Genitalia: Penis subcylindrical, contorted before passing into the epiphallus without external differentiation. Flagellum contorted subdistally, with a short, distally attached retractor muscle; ca. 1/3 the length of the penial complex. The vas deferens is attached to the penial complex, slightly darker in colour and relatively broad. Vagina short; spermathecal duct subcylindrical, its upper part somewhat slenderer before passing into the globose spermatheca.

Exterior of animal: Two living specimens of this new species were kept alive for more than three months in the laboratory. The colour of the animal is brownish- to yellowish-beige, with a slightly darker band on the dorsal side; the rim along the foot is also slightly darker ( Fig. 3 ). In one of the animals the ocular tentacles were greyish-blackish towards the tips, in the other uniformly beige.

Ecology. The type material was collected on the floor of a canyon covered with a dense Bonnetia forest and low vegetation ( Fig. 5 F, 5G). Specimens described here were found on Brocchinia tatei (Bromeliaceae) .

Type material. Holotype RMNH 114233, Venezuela, Estado Bolivar, Chimantá massif, Churí-tepui, Sima Nor-oeste, 2100 m, J. Schlögl leg., ii.2009. Paratypes, same data as holotype, RMNH 114234/1, 114195/ 1 juv., MZSP 92470/1, UF 434148/1.

Comparison with other taxa. This new taxon is conchologically similar to Plekocheilus (P.) fulminans alticola Haas, 1955 and P. (P.) fulminans linterae (Sowerby, 1890) , both known from other tepui sites in Venezuelan Guayana ( Breure 2009). It differs from alticola in (1) the absence of reddish-brown zig-zag streaks, and (2) being smaller. It differs from linterae in (1) being smaller, and (2) being stouter. Compared to both taxa, the columellar fold in P. vlceki is less pronounced.

Remarks. The extremely thin shell of one juvenile shows undulating reddish streaks on a light brown background. This may indicate that in this taxon the uniform colour of the shell is only reached in adulthood.

Etymology. Named in honour of Lukáš Vlček (Bratislava), a member of the Slovakian expedition that explored Chimantá in 2009. He discovered the snails at the localities where material of the taxa described in this paper was collected.

Figures

FIGURE 2. Shells of Plekocheilus spp. A – C. P. (P.) vlceki spec. nov., holotype RMNH 114233. D – G. P. (Eurytus) breweri spec. nov., holotype RMNH 114235. Scale bar = 1 cm.

FIGURE 3. Living specimens of Plekocheilus spp. A – B. P. (P.) vlceki spec. nov., under laboratory conditions. C – D. P. (E.) breweri spec. nov., under natural conditions.

FIGURE 5. Habitat and localities of Plekocheilus species treated in this paper. A. Aerial view of Churí-tepui and surroundings from the North-east. B. Brocchinia with a flowering Utricularia humboldtii inside. C. Habitat of P. breweri spec. nov., showing Bonnetia trees. D. Snail inside Brocchinia hechtioides. E. Bird nest in Cave Juliani where empty shells of P. breweri were found on the ground below. F – G. Overview of Sima Nor-oeste, type locality of P. (P.) vlceki spec. nov.