Phialodonta aviana Herbert, 2020, gen. et sp. nov.
Creators: name: Herbert, David G.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Charopidae
Phialodonta
Phialodonta aviana

description: Phialodonta aviana gen. et sp. nov.
urn:lsid:zoobank.org:act: 82C94EDA-3DF6-444B-8490-0ED744917CD0
Figs 14, 15 I–M, 19E–F
Diagnosis
Shell small, spire raised; protoconch lacking axial sculpture; teleoconch sculpture of distinct, close-set, compound axial riblets, intervals with finer intermediaries and extremely fine, close-set spiral threads; aperture lacking visible dentition; all dentition deeply recessed, comprising two low, rounded, inrunning parietal ridges and three in-running, ridge-like palatal denticles, visible by transparency; basocolumellar dentition lacking; umbilicus wide. Shell pale corneous-brown to honey-brown when fresh; diameter up to 1.55 mm.
Etymology
From the Latin avium: a desert, wilderness; with reference to the Wilderness region, W. Cape.
Material examined
Holotype SOUTH AFRICA • W. Cape, Wilderness area, Woodville ‘ Big Tree’; 33.933° S, 22.650° E; 265 m a.s.l.; 1 Oct. 2002; J.P. Marais leg.; indigenous forest, in leaf-litter; diameter 1.4 mm, height 0.71 mm; NMSA W624/T4246.
Paratypes SOUTH AFRICA – W. Cape • 8 specimens; Wilderness Nat. Park, Kaaimansrivier; 33.98921° S, 22.55130° E; 25 m a.s.l.; 11 Mar. 2005; A. Moussalli and D. Stuart-Fox leg.; indigenous forest, in leaf-litter; NMSA W3524/T4247 • 6 specimens; Wilderness area, Touwsrivier valley; 33.98348° S, 22.60948° E; 30 m a.s.l.; 13 Mar. 2005; A. Moussalli and D. Stuart-Fox leg.; indigenous forest, in leaf-litter; NMSA W3511/T4248 • 11 specimens; Knysna Forest, Diepwalle region, Ysterhout site; 33.967° S, 23.150° E; 380 m a.s.l.; 28 Apr. 1997; D.G. Herbert leg.; indigenous forest, sorted from leaflitter; NMSA V4708/T4245.
Other material
SOUTH AFRICA – W. Cape • 1 specimen; Wilderness Nat. Park, Big Tree area; 33.93661° S, 22.64421° E; 244 m a.s.l.; 6 Mar. 2005; A. Moussalli and D. Stuart-Fox leg.; indigenous forest, in leaflitter; NMSA W2975 • 3 specimens; same collection data as for holotype; NMSA P1011 • 23 specimens; Knysna, start of Prince Alfred’s Pass, just inland from town; 33.996° S, 23.117° E; 360 m a.s.l.; 28 Apr. 1997; D.G. Herbert leg.; indigenous forest; NMSA V4983 • 13 specimens; Nature’s Valley, Salt River area; 33.983° S, 23.533° E; ± 50 m a.s.l.; 19 Sep 2003; D.G. Herbert leg.; indigenous forest; NMSA W1188.
Description
Shell small, diameter up to 1.55 mm, H/D ratio ±0.5; spire raised, whorls tightly coiled; last adult whorl slightly descendant; suture narrowly indented, somewhat sunken; periphery evenly convex. Protoconch comprising apical cap plus approx. 1.0 whorl; diameter ±360 μm; smooth to microscopically shagreened, lacking axial sculpture. Teleoconch of up to 3.25 whorls; sculptured by distinct, close-set, compound axial riblets, with ±5 finer, intermediary axial threads; intervals between riblets approx. twice riblet width at whorl periphery; spiral sculpture of extremely fine, close-set threads more or less throughout. Umbilicus wide. Aperture broadly lunate, lacking any visible dentition; all dentition deeply recessed; parietal region with two low, rounded, in-running ridges, lower one stronger; baso-columellar region lacking dentition; palatal region with three in-running, ridge-like denticles visible by transparency, one just above mid-whorl, one basal and the third between these. Shell pale corneous-brown to honey-brown when fresh.
Distribution and conservation
A narrow-range endemic (Fig. 14), known only from the coastal hinterland in the Outeniqua–Tsitsikamma region, in the environs of Wilderness, Knysna and Nature’s Valley, from the coast to 380 m a.s.l.; in leaflitter of southern afrotemperate forest. The forests in this region fall within the Garden Route National Park and are thus afforded a high degree of protection.
Remarks
As in Phialodonta perfida gen. et comb. nov., the internal dentition of P. aviana gen. et sp. nov. is recessed to such an extent that it is not visible in undamaged apertural view. The palatal denticles, however, are visible externally by transparency, but the parietal lamellae can only be seen if the palatal region is broken back. Phialodonta perfida gen. et comb. nov. differs from the present species in having a single, inwardly broadening, parietal lamella and only two palatal ridges. It also attains a larger size. P. perfida gen. et comb. nov. is only recorded from the Grahamstown area, and the known ranges of the two species are separated by a distance of over 300 km.
The easternmost population of P. aviana gen. et sp. nov. in the Nature’s Valley area is unusual in that some individuals have four palatal denticles instead of three, the upper two of which are distinctly longer than the lower two. In other respects, however, they are identical to typical specimens from the Knysna–Wilderness area. This population is also noteworthy in that it shows that P. aviana gen. et sp. nov. and P. rivalalea gen. et sp. nov. are parapatric, perhaps even sympatric, in the vicinity of Nature’s Valley. Additional survey work is needed to further explore this issue. The differences between the two are discussed in the remarks pertaining to P. rivalalea gen. et sp. nov.
description: Published as part of 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, pp. 1-55 in European Journal of Taxonomy 629 on pages 41-42, DOI: 10.5852/ejt.2020.629, http://zenodo.org/record/3762280