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species

Plekocheilus nebulosus Breure, 2009

kingdom Animalia - animals »  phylum Mollusca - mollusks »  class Gastropoda - gastropods »  order Pulmonata - pulmonates »  family Amphibulimidae »  genus Plekocheilus

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Plekocheilus nebulosus

Author: Breure, A.S.H.

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Description

Diagnosis. Shell sculptured on the last whorl with horizontal threads of various length, often anastomosing; colour pattern with darker spots on the uniform brownish ground colour; aperture decidedly descending in front, peristome somewhat thickened and reflexed.
Description. Shell up to 62.5 mm, 2.0 times longer than wide, imperforate, sides slightly convex, thin to rather solid. Colour golden- to chestnut-brown, with irregularly placed dark-brown spots; upper whorls lighter, purplish, usually eroded. Surface (rather) shining, upper whorls with spirally incised lines, faintly crossed by vertical incisions; on the last whorl this sculpture is more conspicuous, resulting in horizontal threads of various lengths, often anastomosing; in some specimens, the vertical incisions are relatively stronger, breaking the threads into coarse granules; axial growth wrinkles at irregular spaces. Protoconch smooth (eroded). Whorls 4.6, the upper whorls hardly convex, the last whorl much more convex; suture well impressed, somewhat crenulated, deeply descending in front. Aperture elongate-ovate, pointed above, with dark-brown spots visible at the inside, 1.8 times longer than wide, 0.51 times the total length; peristome somewhat thickened and reflexed, whitish. Columellar margin hardly curved, entering the aperture with a slight fold. Parietal wall with a thin, whitish callus.
Ecology. Living specimens have been collected in bromeliad scrub forest. This "Neblinaria scrub" is composed primarily of one species, Bonnetia maguiereorum (Clusiaceae), which forms dense stands of plants 2—3 m tall. The plants have terminal rosettes of leathery leaves that can hold considerable water.
Comparison with other taxa. This novelty seems closely related to Plekocheilus (Eurytus) sophiae spec, nov., from which it differs in (1) being more slender; (2) the aperture more descending in front; (3) the darker spots in the colour pattern. It differs from P. (E.) mundiperditi Haas, 1955 in (1) the sculpture of the last whorl being more thread-like; (2) the aperture deeply descending in front. It has also been compared to the lectotype of P. (E.) superstriatus (Sowerby, 1890), from which it differs in (1) being smaller (51.9 vs. 64.5 mm); (2) lacking the whitish spots in the colour pattern; (3) having the aperture regularly rounded.
Remarks. The sculpture of the last whorl is similar to that of P (E.) sophiae, suggesting it to be a sibling species.
Breure, A.S.H., 2009. New Orthalicidae (Mollusca, Gastropoda) from Venezuelan Guayana: unravelling secrets from the Lost World
Author: Jan Delsing

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