Plekocheilus (Eurytus) nebulosus, Breure, Abraham S. H., 2009

Breure, Abraham S. H., 2009, New Orthalicidae (Mollusca, Gastropoda) from Venezuelan Guayana: unravelling secrets from the Lost World, Zootaxa 2065, pp. 25-50 : 38-39

Plekocheilus (Eurytus) nebulosus spec.nov.

( Figs 2 E─F, 3, 5G─I, 9D)

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 (further dimension given in Table 1 ), 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.

Genitalia. Penis subcylindrical, slightly swollen distally and somewhat constricted at the transition to the epiphallus, which is relatively long and contorted at the junction of the vas deferens that is adhered to and as long as penis and epiphallus. Flagellum thin and slightly tapering, a very thin retractor muscle distally attached. Vagina slightly swollen, short, spermoviduct distally contorted. Spermathecal duct subcylindrical, its intermediate part hardly dilated, tapering towards the elongate-globose spermatheca, which is pigmented. One specimen (UF 284717) was found with fully extended penis ( Figs 3 A─B), showing the slightly swollen base of the penis and the sculpture of the epiphallus and around the genital pore.

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.

Type material. Venezuela, Estado Amazonas, Cerro de la Neblina massif, 3 km NE Pico Phelps, Camp II [00° 49’ 40” N 65° 59’ 00” W], 2085─ 2100 m, R.W. McDiarmid leg., 28─ 31.ii.1985, in Brocchinia plants. Holotype UF 284723, paratypes: Ibidem ( RMNH 112028 /2, UF 284716/2, 284717/2, 284718/1, 284724/1); Ibidem, 5.3 km NE Pico Phelps at the base of the escarpment 1 km NE Pico Maguire, Camp VII [00° 50’ 40” N 65° 58’ 10” W], ca. 1800 m, R.W. McDiarmid leg., 31.i ─ 10.ii.1985 (UF 284731/1, 284732/1, 284737/1); Ibidem, ridge on E slope of Pico Maguire, 2000 m, F.G. Thompson leg., 17.iv.1984, in and under bromeliads (UF 284766/1, 284767/1); Ibidem, ridge at Brazil-Venezuelan border divide [00° 53’ N 65° 56’ W], 2000 m, T. Plowman & W. Thomas leg., 16.iv.1984, on north slope in bromeliad shrub forest (UF 284762/1, 284765/ 1).

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 (Fig. 9D) is similar to that of P. (E.) sophiae , suggesting it to be a sibling species.

Etymology. Latin nebula, cloud; referring to the type locality, where misty weather prevails most of the year.

Figures

FIGURE 2. Genitalia in Plekocheilus (Eurytus). A. P. (E.) t a te i Haas, 1955, FMNH 50346; B ─ D. P. (E.) huberi spec. nov., UF 284746; E ─ F. P. (E.) nebulosus spec. nov., UF 284723. Scale bar— 5 mm.

FIGURE 3. Plekocheilus (Eurytus) nebulosus spec. nov., extended penis UF 284717. A. Dorsal view; B. ventral view.