Plekocheilus (Eurytus) labiosus, Borrero, Francisco J. & Breure, Abraham S. H., 2011

Borrero, Francisco J. & Breure, Abraham S. H., 2011, The Amphibulimidae (Mollusca: Gastropoda: Orthalicoidea) from Colombia and adjacent areas, Zootaxa 3054, pp. 1-59 : 47-48

Plekocheilus (Eurytus) labiosus spec. nov.

(Figs 12A, 18H–I)

Diagnosis. A medium-sized Plekocheilus (Eurytus) characterized by a very expanded and reflexed peristome, sculpture of fine longitudinal growth striae, and well defined columellar fold.

Description. Shell 40.2 mm, about 1.63 times longer than wide, imperforate, ovate, sides strongly convex, relatively thick. Periostracum very thin, honey in color. Shell color pattern consisting of irregularly arranged light brown blotches, but these do not coalesce into a pattern. Surface (hardly) shining, sculptured with more or less regularly spaced, fine axial growth striae (37 to a centimeter in the ventral portion of the last whorl). Each stria consists of series of short sections or elongated granules, regularly interrupted by lower and shorter longitudinal sections, giving the impression that the striae are “beaded,” quite noticeable under magnification. The lower sections are also arranged in a uniform manner, so a spiral pattern of grooves is formed, only evident under magnification. This pattern is present in all sub-apical whorls, but is stronger in the body whorl. Protoconch partly eroded, but with what may be a granular sculpture, thus not inconsistent with that typical of Plekocheilus (Eurytus) ( Breure 1979) . Whorls 5.5, convex, more so the last whorl; suture simple, impressed, hardly descending, going up again before the attachment of the outer lip to the last whorl. Aperture sub-ovate, about 1.6 times as long as wide and about 0.69 times the total shell height; color within light brown, with a few irregular spots of the same color as those in the external coloration. Columellar margin straight initially, then bending to an angle of about 140° between the upper and lower portions; a well defined columellar fold is present midway. Peristome very expanded and reflexed, but not thickened; the widest portion approximately 1/6 of the aperture width. Parietal wall with a thin, white callus.

Dimensions in mm: holotype H 40.2, D 24.7, HA 27.7, WA 17.2, LW 34.5, 5.5 whorls. Paratype H 74, D 43, HA 59.2, WA 33, LW 64.7, 5.5 whorls.

Type locality. Colombia, Cundinamarca, Parque Nacional Chingaza, Embalse de Chuza [04°37’N 073°43’W], ~ 3100 m.

Type material. Holotype UVZ 97034, C. Alvarez leg., ii.1997. Paratype: UMMZ 13843, “ Colombia,” ex Stearns Colln.

Remarks. This new taxon resembles P. (E.) pulicarius in general shape, size and sculpture. P. pulicarius exhibits a wide variation in coloration, the lighter forms being similar to P. labiosus . It is easily distinguishable from P. pulicarius in that P. labiosus has a considerably wider, more expanded peristome.

The holotype is a partially worn shell, bleached mostly dorsally and laterally, lacking part of the periostracum. The paratype is in better condition, with the periostracum nearly complete, but lacks precise locality information. The paratype is substantially larger than the holotype, but the shape of the shells and ratios among the measurements presented above are remarkably similar. Describing this species on the basis of only two shells and a single locality is justified on the basis of the unique features exhibited by this new taxon. No other species of Plekocheilus from northwestern South America has a similar dramatically expanded and reflexed peristome, making it unique and novel. The type locality is not exactly precise, as the specimen was collected dead, presumably on the side of Embalse Chuza, and the elevation given is approximate. Plekocheilus (A.) succineoides co-occurs with P. labiosus at this general locality; this species has a wide distribution mainly in the Altiplano Cundi-Boyacense; the two species are easily separated by shape, sculpture and coloration.

Ecology. The holotype was found “between stones, with grasses and isolated trees.”

Etymology. labiosus (Latin) , having large lips. The name refers to the remarkably expanded peristome of this species. The specific epithet is an adjective.