Plekocheilus (Eurytus) Albers 1850
Creators: name: Breure, Abraham S. H.
name: Schlögl, Jan
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Orthalicidae
Plekocheilus

description: Subgenus Plekocheilus (Eurytus) Albers, 1850
Type species: Helix pentadina Orbigny, 1835 Plekocheilus (Eurytus) breweri spec. nov. (Figs 2 D–2G, 3C, 3D, 4B–4F)
Diagnosis. A medium-sized species of Plekocheilus (Eurytus) characterized by having oblique stripes of reddish- to blackish-brown, often with a yellowish ‘shadow’ besides the stripes on the last whorl. Sculptured with spiral, puckered bands of oblong granules.
Description. Shell: Up to 41.7 mm high, 1.84 times longer than wide, imperforate, slenderly ovate, sides of spire hardly convex, rather thin. Colour yellowish- to (light) chestnut-brown, with descending oblique, partly zig-zag stripes of reddish- to blackish-brown, on the penultimate whorl narrow, on the last whorl with a yellowish ‘shadow’ besides the darker stripes; upper whorls lighter, whitish, eroded. Surface hardly shining, upper whorls with growth striae, on the penultimate and last whorl also with spiral series of oblong granules, forming puckered bands (Fig. 2 G). Protoconch smooth (eroded). Whorls 4.1, rather flat, the last whorl decidedly swollen; suture impressed, somewhat descending in front. Aperture elongate-ovate, somewhat pointed above, the stripes from the outside shining through, whitish inside, 1.60 times longer than wide, 0.54 times the total length; peristome thin and hardly reflexed, whitish. Columellar margin slightly curved, with a very weak fold above, hardly and narrowly dilated above. Parietal wall with a thin, whitish callus.
Genitalia: Penis subcylindrical, distally with a somewhat swollen appendix, passing subdistally into the long epiphallus, which is partly contorted and tapering towards the transition to the flagellum. The flagellum is somewhat tapering, ca. 1/8 the total length of the penial complex. A small retractor muscle is distally attached. The vas deferens is free, shorter than the length of the penis and epiphallus. Vagina short; proximal part of spermathecal duct subcylindrical, its intermediate part widened before distally tapering towards the globose spermatheca. Spermoviduct very contorted; albumen gland moderately long.
The internal morphology is simple in cross-sections (Figs. 4 D, 4E). All parts of the penial complex have longitudinal folds (Fig. 4 F). The epiphallus enters the penis below the distal end (Fig. 4 Ee). The vagina is actually shorter than it appears, as the bifurcation of spermathecal duct and spermoviduct is masked externally (Fig. 4 Eb).
Ecology. This species was collected on the summit plateau in stands of Brocchinia hechtioides (Bromeliaceae; Fig. 5 C), where it was found up to 1 m high. Living specimens are dark-grey to blackishbodied (Figs 3 C–D). Some specimens were found in Brocchinia tatei on the bottom of a canyon, 120 m deep, called Sima Nor-oeste (Figs 5 F–G). Snails were observed inside the Brocchinia plants during day-time (Fig. 5 D); in the evening they became active and were seen feeding on the leaves of these plants (Brewer-Carias, pers. comm.). Brocchinia is adapted to low-nutrient soils such as those of the tepuis, often rooted in plant debris on the barren rocks. Other plant species observed in this tubiform meadow community (sensu Huber 1995b), were the cup-shaped carnivorous Heliamphora minor (Sarraceniaceae) and the spiny rosettes of Orectanthe ptaritepuyana (Xyridaceae). Brocchinia hechtioides, which provides shelter to the snails, also frequently hosts Utricularia humboldtii (Lentibulariaceae) (Fig. 5 B). This endemic species is carnivorous, too (Brewer-Carias 1978). Carnivory in plants is characteristic of conditions where light and moisture are abundant, but soil macronutrients, especially nitrogen, phosphorus and potassium, are severely limited (Givnish et al. 1984, Ellison 2006). Givnish et al. (1984) suggested that the genus Brocchinia is considered “in its way to carnivorism.” It is now suggested that the excrements of the snails—together with those of a Prismantis frog species that was also found sheltering in Brocchinia plants—adds to the debris from the insectivorous Utricularia and act as an additional nitrogen source that gives these plants a better competitive edge (Brewer-Carias, pers. comm.).
Type material. Venezuela, Estado Bolívar, Chimantá massif, Churí-tepui: Holotype RMNH 114235, 0 5°16'44.9"N 0 62°00'56.35"W, 2405 m (Fig. 1 C locality 2 = type locality), J. Schlögl leg., ii.2009. Paratypes: same data as holotype, CB/2, MLSC /4, MZSP 92471/2, RMNH 114236/18, 114238/4 alc., SNMSZ 6892– 6895, UF 434147/3; Sima Nor-oeste, 2285 m (Fig. 1 C locality 1), J. Schlögl leg., ii.2009. RMNH 114237/1 alc.; ibidem, B. Smida leg., JG/3, RMNH 114246/2.
Comparison with other taxa. This novelty seems conchologically similar to Plekocheilus (Eurytus) fusitorsus (Oberwimmer, 1931), but differs in (1) the sculpture on the last whorl; (2) being smaller (41.7 vs. 63.3 mm); (3) the less shining surface. It may also be compared to P. (E.) mundiperditi Haas, 1955, from which it differs in (1) being smaller (41.7 vs. 47.3 mm); (2) being more slender; (3) the different colour pattern.
Etymology. We take much pleasure to dedicate this species to Charles Brewer-Carias (Caracas), who during many years has stimulated scientific research in the Guayana Highlands and who has led many expeditions to this area.
description: Published as part of 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), pp. 51-60 in Zootaxa 2416 on pages 57-58, DOI: 10.5281/zenodo.293891