Phialodonta aviana, 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 : 41-42

publication ID	https://doi.org/ 10.5852/ejt.2020.629
publication LSID	lsid:zoobank.org:pub:ECEBD539-6E3E-45BE-A0CB-264DF3270CC0
DOI	https://doi.org/10.5281/zenodo.3804748
persistent identifier	https://treatment.plazi.org/id/82C94EDA-3DF6-444B-8490-0ED744917CD0
taxon LSID	lsid:zoobank.org:act:82C94EDA-3DF6-444B-8490-0ED744917CD0
treatment provided by	Valdenar
scientific name	Phialodonta aviana
status	gen. et sp. nov.

Treatment

Phialodonta aviana View in CoL gen. et sp. nov.

urn:lsid:zoobank.org:act:82C94EDA-3DF6-444B-8490-0ED744917CD0

Figs 14 View Fig , 15 View Fig 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. GoogleMaps

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 GoogleMaps • 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 GoogleMaps • 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 GoogleMaps .

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 View Materials GoogleMaps • 3 specimens; same collection data as for holotype; NMSA P1011 View Materials GoogleMaps • 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 View Materials GoogleMaps • 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 View Materials GoogleMaps .

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 View Fig ), 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.