Avakubia crystallum 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 : 630-632

Avakubia crystallum de Winter , sp. n.

Figs 13, 18G, H

Gulella (Avakubia) cf. avakubiensis: de Winter 1995: 225 .

Etymology:The species name is a noun in apposition and refers to the type locality (Monts de Cristal), as well as to the glassy, gem-like appearance of the fresh shell (especially with the red softparts inside), which, however, is not unique for this species.

Diagnosis: Resembles A. fruticicola , especially by its (slightly less) close-set teleoconch ribs, but this species has a smaller, less elongate shell with less rapidly expanding whorls, less sharp apical angle and spire angle, proportionally larger body whorl, and differs in protoconch sculpture. The shell of A. biokoensis is larger and more oval, with a smaller number of spiral cords on the protoconch; the shell of A. occidentalis is similarly shaped, but has a less densely ribbed teleoconch, tighter coiled whorls and different protoconch sculpture; A. crystallum resembles A. avakubiensis only superficially, differing by a larger shell with much less widely spaced ribs, as well as in details of the protoconch sculpture.

Description:

Shell ( Figs 13, 18G, H, Table 1): Medium-sized (mean H 3.7 mm), ovate-biconical, largest width at penultimate whorl. H:D in holotype 1.79, in other specimen 1.79. Whorls expanding rather fast: coiling tightness in holotype 4.1, in other specimen ca 4.0. Whorls moderately convex.Apex slightly pointed. Protoconch consisting of ca 2.0 whorls, second protoconch whorl convex, contour resembling that of A. avakubiensis . Protoconch sculpture of holotype consists of 15 regularly spaced spiral cords on last protoconch whorl, each 6.2–8.5 µm wide, without noticeably thinner lines between them. Spiral cords made up of adjoining but distinct particles of variable length, but generally longer than wide. Teleoconch sculpture of rather close-set, curved, slightly oblique axial ribs, ca 10.7 ribs/mm on penultimate whorl in holotype, 11.1 ribs/mm in other specimen, with fine spirals in interstices. Last whorl takes up half the shell height or less, in holotype BWH 50% of H, in other specimen 47%. Peristome complete in holotype (not in other specimen, measurements are estimates), somewhat higher than wide, PH:PW in holotype 1.15, in other specimen 1.08. PH 37% of H in holotype, in other specimen 29 %. PW 58% of D in holotype, in other specimen 49 %. Apertural lip holotype expanded and flaring, slightly reflected and somewhat incrassate. Two apertural barriers visible in aperture: a weak, thickening on mid-palatal wall and a slightly projecting angular tooth that extends inwards as deeply entering lamella. Internal palatal wall of body whorl with a deep-set palatal fold (no longer visible in coated holotype, nor in other specimen which is worn). Columellar lamella not visible in aperture. Umbilicus narrow but open .

Body colour: Holotype with conspicuously pinkish red coloured soft parts (collector’s observation).

Anatomy: Unknown.

Holotype: GABON: Région Estuaire: Monts de Cristal , ca 5 km N of Kinguélé, 0.5°N 10.3°E, 400 m, 26.xii.1989 J.J. Wieringa, wet rocky slope in rainforest ( RMNH.MOL.330185).

Other material examined: GABON: Région Ngounié: 1 ad. dry shell, Ofoubou area , ca 30 km W of Mandji, 1.75°S 10.10°E, ca 50 m, vii.1991, J. Reitsma, rainforest ( RMNH.MOL.330186) .

Distribution ( Fig. 11): Western Gabon.

Habitat: The holotype was collected from a Begonia plant ( B. letouzeyi Sosef ) growing on a wet rock along a stream in undisturbed rainforest at 400 m. The other specimen, an eroded empty shell, was found in a leaf-litter sample in undisturbed lowland rainforest.

Remarks: This species is somewhat intermediate between A. fruticicola and A. biokoensis in shell size and rib sculpture. In shell shape it best resembles A. occidentalis . Still, the two western Gabonese shells appear to be recognisable by a number of characters, and we prefer to treat these specimens as a new species, also in view of the considerable (300 to 1200 km) geographic separation between the known localities of these species and those of A. crystallum . Specimens reported from Central Gabon by Fontaine et al. (2007) are clearly not conspecific with A. crystallum , and more closely resemble A. avakubiensis (as discussed there).