Afrodonta bilamellaris Melvill & Ponsonby, 1908

Herbert, David G., 2020, Revision of the aperturally dentate Charopidae (Gastropoda: Stylommatophora) of southern Africa - genus Afrodonta s. lat., with description of five new genera, twelve new species and one new subspecies, European Journal of Taxonomy 629, pp. 1-55 : 5-7

Afrodonta bilamellaris Melvill & Ponsonby, 1908

Figs 1 A–C, 2, 17A–B

Afrodonta bilamellaris Melvill & Ponsonby, 1908: 134 , pl. 7, fig. 6.

Afrodonta bilamellaris londonensis Solem, 1970: 359 , fig. 2c–d. Syn. nov.

Afrodonta bilamellaris – Godwin-Austen, in Melvill & Ponsonby 1908: 135. — Connolly 1939: 251, text-fig. 19 (1). — Herbert & Kilburn 2004: 249, text-fig.

Endodonta [ Endodonta (Afrodonta) ] bilamellaris – Burnup 1912: 335, pl. 24, fig. 18.

Endodonta (Afrodonta) bilamellaris – Connolly 1912: 127.

Afrodonta bilamellaris bilamellaris – Solem 1970: 358, fig. 2a–b.

Diagnosis

Shell small, spire slightly raised, whorls slightly flat-sided; protoconch smooth, at most microscopically shagreened (diameter ±315 μm); teleoconch texture silky; sculpture comprising simple, very fine and close-set axial riblets, tending to alternate in strength; spiral sculpture of faint threads in riblet intervals; parietal region with a single well-developed, in-running lamella (sometimes bifurcating posteriorly); baso-columellar region with a well-developed, in-running ridge-like denticle; palatal region usually lacking dentition (exceptionally with a weak supra-peripheral ridge); umbilicus relatively narrow. Shell pale honey-coloured when fresh; diameter up to 1.7 mm.

Material examined

Afrodonta bilamellaris bilamellaris Melvill & Ponsonby 1908

Lectotype (by inference, Connolly 1912: 128)

SOUTH AFRICA • KwaZulu-Natal; NHMUK 1908.12.14.54 .

Two localities were cited in the original description, Dargle and Edendale Falls; Connolly (1939) stated that the ‘type’ was from Dargle, but both the NHM register and labels cite Edendale Falls as the locality for lot 1908.12.14.54.

Paralectotypes

SOUTH AFRICA – KwaZulu-Natal • 1 specimen; same collection data as for lectotype; NHMUK 1908.12.14.55 • 3 specimens; same collection data as for preceding; NHMUK 1937.12.30.2723 to 2725 • 1 specimen; Dargle ; H.C. Burnup leg.; NMSA 2182/T610 .

Afrodonta bilamellaris londonensis Solem, 1970

Holotype

SOUTH AFRICA • E. Cape, East London, Signal Hill ; NMSA 4359/T1183 .

Paratypes

SOUTH AFRICA – E. Cape • 2 specimens; same collection data as for holotype; NMSA 4360/T1184 ; • 2 specimens; same collection data as for preceding; FMNH 159054 .

Distribution and conservation

Endemic to south-eastern South Africa ( Fig. 2 ), ranging widely from central KwaZulu-Natal (Zinkwazi), through E. Cape to eastern W. Cape (Knysna area); in E. Cape and W. Cape it is confined to forests in the coastal hinterland, but in KwaZulu-Natal it ranges inland to the southern mistbelt forests of the Midlands. Inhabits a range of forest and dense thicket-like habitats, from the coast to 1500 m a.s.l., living in leaf-litter. Not of conservation concern.

Remarks

Solem (1970) described smaller, strongly dentate specimens from East London as a separate subspecies, Afrodonta bilamellaris londonensis , and similar specimens have been found subsequently at other localities (Port St Johns area, Tsitsikamma and Knysna). However, the reported differences between the subspecies are a matter of degree and I have not found it possible to discriminate consistently between the two. This, in conjunction with the fact that the records of strongly dentate londonensis specimens are not geographically circumscribed and spatially separated from the nominotypical form, leads me to conclude that the two do not represent distinct entities and that Af. bilamellaris is simply a variable species in terms of the strength of the apertural dentition. This variation occurs to some extent within as well as between populations. In one strongly dentate londonensis population from the Port St Johns area, some individuals evince traces of palatal dentition in the form of a weak supra-peripheral ridge or denticle and occasionally an even weaker sub-peripheral one.

Figures

Fig. 1. Shells of Afrodonta species. A–C. Af.bilamellaris Melvill & Ponsonby, 1908, Karkloof, KwaZulu- Natal, diameter 1.45 mm (NMSA W8721). D–F. Af. connollyi Solem, 1970, Middledrift, Thukela Valley, KwaZulu-Natal, diameter 1.52 mm (NMSA V4985). G–J. Af. farquhari (Burnup, 1912), Gamtoos River mouth, E. Cape, diameter 1.39 mm (NMSA W8688). K–N. Af. geminodonta sp. nov., holotype, diameter 1.36 mm (NMSA V9891/T4241).

Fig. 2. Distribution of Afrodonta bilamellaris Melvill & Ponsonby, 1908 (blue circles) and Af. connollyi Solem, 1970 (orange squares). Contour at 1000 m.