Avakubia occidentalis de Winter, 2013

de Winter, A. J. & Vastenhout, N., 2013, Revision of the Afrotropical land snail genus Avakubia Pilsbry, 1919, with description of Pseudavakubia gen. n. and eleven new species (Gastropoda: Pulmonata: Streptaxidae), African Invertebrates 54 (2), pp. 605-663 : 635-637

Avakubia occidentalis de Winter , sp. n.

Figs 16, 21C, D

Etymology: From Latin occidentalis (western), in reference to the westernmost distribution of this species among any known Avakubia species.

Diagnosis: A small species of Avakubia , differing from similar-sized congenerics by a combination of conchometrical characters, as well as by the large number of spiral cords on the protoconch.

Description:

Shell ( Figs 16, 21C, D, Table 1): Small to medium-sized (mean H 3.3 mm), subcylindrical, largest width at penultimate whorl. H:D 1.59–1.84, in holotype 1.84. Number of whorls 5–5.5. Coiling tightness 4.45–4.65, in holotype 4.45. Whorls moderately convex. Protoconch slightly acuminate, consisting of ca 2 whorls. Protoconch on second whorl with>16, more or less regularly spaced cords, 6.3–8.6 µm wide, without finer spiral lines between them. Spiral cords made up of series of adjoining, poorly differentiated rectangular particles of variable length (ca 8–19 µm). Teleoconch sculpture of regularly spaced, curved axial ribs, 9.0–10.0 ribs/mm on penultimate whorl, median 9.9 ribs/mm, in holotype 9.0, with fine spirals in interstices. BWH 48–49 % of H, in holotype 48%. Peristome holotype entire (peristome of other shells damaged, PW measurements not accurate). PH:PW 0.88–1.10, in holotype 1.06. PH 32–34 % of H, median 34 %, in holotype 34 %. PW 52–59% of D, median 56%, in holotype 59%. Apertural lip expanded and flaring, reflected and incrassate in holotype. Two barriers visible in aperture: a blunt, tooth-like thickening on mid-palatal wall and a conspicuous angular tooth that extends inwards as deeply entering lamella. Internal wall of body whorl with deeply-set palatal fold, externally barely visible in opaque shells. Columellar lamella not visible in aperture, but probably present. Umbilicus punctiform but open, slightly wider than in A. fruticicola .

Body colour: Soft parts at least partly reddish (dried-in tissue paratype).

Anatomy: Unknown.

Holotype: GHANA: Volta Region: Logba Tota , 6.88363°N 0.46804°E, 470 m, 30.i.2010, P. Tattersfield, M.E. Nutsuakor & A.J. de Winter, semi­deciduous forest on steep slope near waterfall ( NMW.Z. 2013.055.00001).

Paratype: 1 dry shell, same data as holotype ( RMNH.Mol.254654) .

Other material examined: GHANA: Eastern Region : 1 dry shell, Atewa Range Forest Reserve, 6.12368°N 0.60445°W, 655 m, 23.i.2010, P. Tattersfield, M.E. Nutsuakor & A.J. de Winter, in litter of recently logged high forest ( RMNH.MOL.330190) .

Distribution ( Fig. 17): Known from two localities in eastern Ghana.

Habitat: Found in semi-deciduous forest near waterfall at 470 m, as well as in upland evergreen forest at 650 m. All specimens were collected from the forest floor.

Remarks: This species superficially resembles A. fruticicola in size, teleoconch sculpture and colour of the soft parts. However, the Ghanaian shells differ in a number of characters, such as a more cylindrical shell, tighter coiled whorls (about half a whorl more at the same size), proportionally smaller body whorl, more pointed apex, and slightly wider umbilicus and wider spaced axial ribs, in addition to details of the protoconch sculpture. Two A. occidentalis specimens were found alive on the forest floor, whilst specimens of A. fruticicola were exclusively collected from the understorey vegetation.The Ghanaian localities are situated some 1200 km from those of A. fruticicola in Cameroon.

Avakubia occidentalis is the only Avakubia species known in the Upper Guinea forest block. Traditionally postulated biogeographic barriers like the Dahomey Gap and Cross River have apparently not restricted the distribution of the genus, which might suggest a considerable age for the taxon. On molecular grounds Rowson et al. (2011) suggested Avakubia to be an ancient taxon that possibly survived the Mesozoic ⁄ Cainozoic mass extinctions, whilst the streptaxid diversity is otherwise known from the Cainozoic only.