Phialodonta agulhasae, Herbert, 2020

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 : 38-40

Phialodonta agulhasae gen. et sp. nov.

urn:lsid:zoobank.org:act:C5A5E2C0-CEF1-41DC-B8B2-7095C029E70B

Figs 14 , 15 A–D

Diagnosis

Shell very small, planorboid, spire slightly sunken; protoconch lacking axial sculpture; teleoconch sculpture of close-set axial riblets with extremely fine, close-set spiral threads in their intervals; aperture lacking parietal and baso-columellar dentition, palatal region with three recessed, in-running, ridge-like denticles; umbilicus wide. Shell corneous-brown; diameter up to 1.3 mm.

Etymology

Named after the Agulhas region.

Material examined

Holotype

SOUTH AFRICA • W. Cape, Gansbaai area , Grootbos Private Nat. Res. ; 34.54135° S, 19.43871° E; 8 Oct. 2007; D.G. Herbert and L.S. Davis leg.; station 07-044, afrotemperate forest, in leaf-litter and under logs; diameter 1.3 mm, height 0.61 mm; NMSA W7816/T4257.

Description

Shell very small, diameter up to 1.3 mm, H/D ratio 0.47; planorboid, spire slightly sunken; whorls tightly coiled, not conspicuously deep; last adult whorl not descendant; suture shallowly indented, periphery evenly convex. Protoconch comprising apical cap plus approx. 1.0 whorl; diameter ±320 μm; microscopically shagreened, lacking axial sculpture. Teleoconch of ±3.0 whorls; sculptured by distinct, close-set, axial riblets, intervals between riblets more or less equal to width of riblets at whorl periphery; spiral sculpture of extremely fine, close-set threads in riblet intervals. Umbilicus wide. Aperture lunate, relatively narrow, apical and basal limits rounded; parietal and baso-columellar regions lacking dentition; palatal region with three recessed, in-running, ridge-like denticles, one just above mid-whorl, one just below mid-whorl and one basal. Shell corneous-brown.

Distribution and conservation

A narrow-range endemic ( Fig. 14 ), known only from the type locality; in leaf-litter of southern afrotemperate forest. The type locality lies in a well-managed private nature reserve, but additional Agulhas Plain localities that retain patches of southern afrotemperate forest need to be surveyed in the hope of finding additional extant colonies of this species.

Remarks

The holotype is the only specimen available and though it is not a fresh shell, it is sufficiently distinct to permit its description as a new species. I have refrained from examining it under SEM due to its fragility and thus finer details of its sculpture are not available. On account of its smooth protoconch, relatively distinct axial riblets and wide umbilicus, I refer it to Phialodonta gen. nov. In its planorboid shape it resembles P. introtuberculata gen. et comb. nov., but that species has a proportionately narrower shell (mean H/D ratio 0.424 – Solem 1970) and very different apertural dentition.

Figures

Fig. 14. Distribution of Iterodonta gen. nov. and Phialodonta gen. nov. species. Iterodonta ammonita gen. et sp. nov. (brown triangles), Phialodonta agulhasae gen. et sp. nov. (orange square), P. atromontana gen. et sp. nov. (turquoise square), P. aviana gen. et sp. nov. (royal blue squares), P. introtuberculata (Connolly, 1933) gen. et comb. nov. (red squares), P. perfida (Burnup, 1912) gen. et comb. nov. (green square), P. rivalalea gen. et sp. nov. (pink squares). Contour at 1000 m.

Fig. 15. Shells of Phialodonta gen. nov. species. A–D. P. agulhasae gen. et sp. nov., holotype, diameter 1.30 mm (NMSA W7816/T4257). E–H. P. atromontana gen. et sp. nov., holotype, diameter 1.40 mm (NMSA W9580/T4254). I–L. P. aviana gen. et sp. nov., holotype, diameter 1.40 mm (NMSA W624/ T4246). M. P. aviana gen. et sp. nov., specimen with palatal region broken back to reveal apertural dentition, paratype, Touwsrivier, Wilderness, W. Cape, diameter 1.32 mm (NMSA W3511/T4248).