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

description: Iterodonta ammonita gen. et sp. nov.
urn:lsid:zoobank.org:act: A33983DE-4995-4FB7-A54D-83F7E4F897D8
Figs 13, 14, 19 A–B
Diagnosis
Shell small, symmetrically biconcave; protoconch initially with traces of close-set spiral threads, later portion with spiral threads and close-set axial riblets producing a fine, reticulate sculpture; teleoconch sculpture of close-set, compound axial riblets with finer, uneven intermediary axial threads; aperture lacking parietal and columellar dentition; palatal region with 1–3 broad, prosocline, axial ridge-like calluses set back from lip, visible through translucent shell; umbilicus very wide and shallow. Shell translucent, straw-brown to pale honey-brown; diameter up to 1.68 mm.
Etymology
From ammonite (Ammonoidea); with reference to the symmetrically biconcave shell.
Material examined
Holotype SOUTH AFRICA • W. Cape, Riviersonderendberge, Oubos (Oudebosch); 34.07702° S, 19.82884° E; 440 m a.s.l.; 11 Oct. 2007; D.G. Herbert and L.S. Davis leg.; afrotemperate forest, in leaf-litter and under logs; diameter 1.45 mm, height 0.70 mm; NMSA W5826/T4258.
Paratypes SOUTH AFRICA – W. Cape • 3 specimens; same collection data as for holotype; NMSA P1017/T4259 • 1 specimen; Grootvadersbosch Nat. Res.; 33.98994° S, 20.81658° E; 345 m a.s.l.; 13 Oct. 2007; D.G. Herbert and L.S. Davis leg.; afrotemperate forest, in leaf-litter and under logs; NMSA W5899/ T4256.
Description
Shell small, diameter up to 1.68 mm, H/D ratio ±0.48; symmetrically biconcave, whorls tightly coiled, but not conspicuously deep; spire sunken, but not deeply so; last adult whorl not descendant; suture strongly indented and apical and basal portions of whorls strongly convex, less so at mid-whorl; periphery evenly convex. Protoconch comprising apical cap plus approx. 1.25 whorls; diameter ±330 μm; initially with traces of close-set spiral threads, later portion with spiral threads and close-set axial riblets producing a fine, reticulate sculpture. Teleoconch of up to 3.5 whorls; sculptured by distinct, close-set compound, orthocline axial riblets with finer, uneven intermediary axial threads; intervals between riblets approx. twice riblet width at whorl periphery; spiral sculpture relatively distinct, comprising microscopic spiral threads, most obvious in intervals between riblets; threads coarsest below suture and in umbilicus, but present throughout. Umbilicus very wide and relatively shallow (Fig. 13B). Aperture narrow, more or less symmetrically lunate, with apical limit rounded; parietal and columellar dentition lacking; palatal region with 1–3 broad, prosocline, axial, ridge-like calluses set back ⅛–½ whorl from lip (position variable), visible through translucent shell (Fig. 13D); calluses slightly curved, one usually well developed, the others in the process of resorption or deposition. Shell translucent, straw-brown to pale honey-brown.
Distribution and conservation
A narrow-range endemic (Fig. 14), known only from the south-facing slopes of the Langeberge and Riviersonderendberge, W. Cape, at 300–450 m a.s.l.; in leaf-litter of southern afrotemperate forest. Grootvadersbosch Nature Reserve is a formally protected area and the indigenous forest of the Langeberge and Riviersonderendberge are generally well managed, with additional formally protected areas that should be surveyed in the hope of finding additional extant colonies of this species.
Remarks
Iterodonta ammonita gen. et sp. nov. is highly distinctive amongst the southern African charopid fauna. The only other African species with similar palatal dentition is Endodonta kempi Connolly, 1925 recorded from Kenya, Malaŵi and Zambia (Bruggen 1988, 2007), but in that species the spire is not sunken, the umbilicus is narrower and the protoconch lacks distinctive sculpture. Solem (1970) referred the latter to Afrodonta, but this seems improbable and its true relationships require further investigation.
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 35-37, DOI: 10.5852/ejt.2020.629, http://zenodo.org/record/3762280