Phialodonta rivalalea 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 rivalalea

description: Phialodonta rivalalea gen. et sp. nov.
urn:lsid:zoobank.org:act: 4F0EED11-370A-4828-9A7A-9C320AA7BCFB
Figs 14, 16 I–L, 19K–L
Diagnosis
Shell small, spire slightly to distinctly raised; protoconch lacking axial sculpture; teleoconch sculpture of close-set, compound axial riblets, intervals with 4–5 finer intermediaries and extremely fine, close-set spiral threads; aperture with two narrow, in-running parietal lamellae and a narrow, in-running basocolumellar ridge; palatal region with three denticles recessed 1 ⁄ 5 – 1 ⁄ 4 whorl behind outer lip; an additional narrow, thread-like ridge immediately below suture evident by transparency; umbilicus very wide, its margin relatively sharply rounded. Shell pale corneous-brown to pale honey-brown when fresh; diameter up to 1.7 mm.
Etymology
From the Latin rivus: a stream, and the Greek laleo (λαλεΟ): to talk, to utter; with reference to the Tsitsikamma region. Tsitsikamma (Outeniqua Khoi): ‘the water that speaks’.
Material examined
Holotype SOUTH AFRICA • W. Cape, Nature’s Valley, Tsitsikamma Nat. Park, at camping ground entrance; 33.9723° S, 23.56306° E; 10 m a.s.l.; 20 Sep. 2004; A. Moussalli and D. Stuart-Fox leg.; indigenous forest, in leaf-litter; diameter 1.68 mm, height 0.79 mm; NMSA W3114/T4251.
Paratypes SOUTH AFRICA – W. Cape • 7 specimens; Nature’s Valley, Tsitsikamma Nat. Park, scenic drive on the way to park office; 33.9703° S, 23.53936° E; 200 m a.s.l.; 16 Sep. 2004; A. Moussalli and D. Stuart-Fox leg.; indigenous forest, in leaf-litter; NMSA W3125/T4253 • 1 specimen, same collection data as for holotype; NMSA P1012/T4252. – E. Cape • 5 specimens; Bloukrans River Valley, eastern side; 33.95377° S, 23.65423° E; 140 m a.s.l.; 21 Sep. 2003; D.G. Herbert leg.; in leaf-litter at base of road cutting through indigenous forest; NMSA W1171/T4249 • 14 specimens; Tsitsikamma Forest, near Paul Sauer Bridge over Storms River; 33.9682° S, 23.92634° E; 260 m a.s.l.; 28 Apr. 1997; D.G. Herbert leg.; sorted from leaf-litter; NMSA V4734/T4250.
Other material
SOUTH AFRICA • 1 specimen; E. Cape, Tsitsikamma Forest, ‘big tree’ west of Storms River bridge; 33.9682° S, 23.8982° E; 260 m a.s.l.; 1 Oct. 2002; J.P. Marais leg.; sorted from leaf-litter; NMSA W1768.
Description
Shell small, diameter up to 1.7 mm, H/D ratio ±0.47; spire slightly to distinctly raised; whorls tightly coiled; last adult whorl descendant; suture narrowly indented, somewhat sunken; periphery evenly convex. Protoconch comprising apical cap plus approx. 1.0 whorl; diameter ±410 μm; microscopically shagreened, lacking axial sculpture. Teleoconch of up to 3.5 whorls; sculptured by distinct, close-set, compound axial riblets, with 4–5 finer, intermediary axial threads; intervals between riblets 1–2 times width of riblets at whorl periphery; spiral sculpture of extremely fine, close-set threads more or less throughout. Umbilicus very wide, its margin relatively sharply rounded.Aperture broadly lunate; parietal region with two narrow, in-running lamellae, the upper one weaker and slightly more recessed; basocolumellar region with a similar recessed, narrow, in-running, lamella-like ridge (sometimes scarcely evident in apertural view); palatal region with three denticles recessed 1 ⁄5– 1 ⁄4 whorl behind outer lip, denticles evident by transparency, but hardly visible in apertural view, one just above mid-whorl, one just below mid-whorl, the third more basal, middle denticle situated slightly closer to aperture and often more elongate (particularly in juveniles); a fourth palatal structure in the form of a narrow, thread-like ridge lying immediately below the suture is evident by transparency in fresh juveniles and subadults. Shell pale corneous-brown to pale honey-brown when fresh.
Distribution and conservation
A narrow-range endemic (Fig. 14), known only from the coastal hinterland in the Tsitsikamma region, southern Cape, from the coast to 260 m a.s.l.; in leaf-litter 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
In terms of the overall facies of the shell, Phialodonta rivalalea gen. et sp. nov. is closest to P. aviana gen. et sp. nov. It differs from the latter in having parietal lamellae that are visible through the aperture, and in possessing a narrow, in-running baso-columellar ridge and a wider umbilicus.
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 49-50, DOI: 10.5852/ejt.2020.629, http://zenodo.org/record/3762280