Chondrocyclus herberti sp. nov.

urn:lsid:zoobank.org:act: 4265F23E-DB10-46D8-B263-E90EA206C53F

Figs 8D, 9, 10 A–B, 12

Diagnosis

Shell very small, moderately depressed; periostracum with widely spaced axial costae bearing broad, distally rounded flanges at the shell periphery; operculum duplex, exterior portion shallowly concave, with step-shaped multispiral lamella terminating in a long solid fringe reflexed over peristome; radula with two large cusps on second lateral tooth.

Etymology

Named for Dai Herbert, Malacologist at the KwaZulu-Natal Museum for 33 years, in recognition of his expertise in South African molluscs and in acknowledgement of his mentorship.

Type material examined

Holotype

SOUTH AFRICA – Eastern Cape • Baviaanskloof, Western Poortjies area; 33.6536°S, 24. 5161°E; 9 Oct. 2000; D. Herbert leg.; riverine thicket, in leaf-litter; NMSA P1043 /T4277. (Fig. 10 A–B)

Paratypes

SOUTH AFRICA – Eastern Cape • 39 specimens; same collection data as for holotype; NMSA V8632 / T4127 • 15 specimens; Baviaanskloof, Poortjies area, rocky bank adjacent to Witte River; 33.6537° S, 24.527°E; 258 m a.s.l.; 26 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; riverine thicket, in leaf litter; ELM D16891/T41 • 1 specimen; same collection data as for preceding; ELM W3691 /T42 • 1 specimen; same collection data as for preceding; NMSA W9279 /T3077 • 2 specimens; same collection data as for preceding; NHMUK 20120285 • 2 specimens; same collection data as for preceding; NMW.Z.2012.065.00012 • 3 specimens; same collection data as for preceding; RMNH MOL.330501 • 16 specimens; Baviaanskloof, Poortjies area; 33.6536° S, 24.5272° E; 9 Oct. 2000; D. Herbert leg.; riverine thicket, in leaf-litter; NMSA V8576 /T4129 • 20 specimens; Baviaanskloof, Geelhoutbos, forest in narrow kloof; 33.6335° S, 24.2449°E; 11 Oct. 2000; D. Herbert leg.; in leaf-litter; NMSA V8763 /T4130 • 9 specimens; Baviaanskloof, Geelhoutbos, near pool and weir, forest in narrow kloof; 33.6430° S, 24.2426°E; 468 m a.s.l.; 9 Mar. 2015; M. Cole leg.; in leaf-litter; ELM D17990/T43 • 34 specimens; Baviaanskloof, Geelhoutbos, near Hikers’ hut, forest in narrow kloof; 33.6356° S, 24.2457°E; 373 m a.s.l.; 9 Mar. 2015; M. Cole leg.; in leaf-litter; ELM D17986/T44 • 1 specimen; Baviaanskloof wilderness area, Grassnek, thicket/fynbos transition; 33.6430° S, 24.2426°E; 11 Oct. 2000; D. Herbert leg.; under stones and amongst leaf litter; NMSA V8648 /T4128 .

Other material examined

SOUTH AFRICA – Eastern Cape • 2 specimens; Baviaanskloof, Western Poortjies area, rocky bank adjacent to Witte River; 33.6542° S, 24. 5160°E; 8 Mar. 2015; M. Cole leg.; riverine thicket, in leaf litter; ELM D17995 .

Description

SHELL (Fig. 12 A–C). Very small, moderately depressed, adult diameter 3.43–4.31 mm, height 2.09– 2.69 mm, diameter:height 1.46–1.94 (n = 20). Spire moderately exserted, protoconch acutely mammillate and tilted (Fig. 12A). Embryonic shell (Fig. 12D) just over two whorls, microscopically malleate for approx. two whorls, axial costae begin to develop just after two whorls. Teleoconch comprising approx. 2.5 whorls, very convex, rapidly increasing, suture impressed. Aperture circular, last whorl descending near aperture, peristome simple, continuous and free. Umbilicus deep, exposing all the whorls. Periostracum glossy, light yellowish-brown and lacquer-like with relatively widely spaced lamellate axial costae at regular intervals, 39–51 (n = 22) on last whorl (Fig. 12 A–C), which produce broad flanges with rounded apices at periphery (Fig. 8D, 12E); intervals between costae with six to nine distinct microscopic axial threads. Shell translucent and corneous when fresh.

LIVING ANIMAL. Very dark grey.

OPERCULUM (Fig. 12 G–H). Duplex, outer portion shallowly concave and consisting of multispiral lamella with 4.5 whorls, each step-shaped and increasing in height towards outside, sloping at growing edge; very long fringe of fused bristles emanates near top of lamellar blade with a slight groove between fringe and lamellar blade; lamellar blade does not project above level of fringe; fringe of each whorl fused to lamella of following whorl.

RADULA (Fig. 12F). Rachidian with five cusps, central one approx. twice length of outer two on each side; first lateral tooth with four cusps and a vestigial fifth, third cusp (from centre) the largest; second lateral tooth with two very large cusps and two small ones on the outer side (outermost sometimes vestigial).

PENIS (Fig. 12I). Shaft more or less cylindrical, distal half slightly expanded on left, intromittent organ short.

Distribution and habitat

Eastern Cape, Baviaanskloof (Fig. 9). Indigenous forest patches in narrow ravines (Western Cape Afrotemperate Forest of von Maltitz et al. 2003) and Albany subtropical thicket (Groot Thicket group) (Hoare et al. 2006), in leaf-litter; also in subtropical thicket/fynbos transition, under stones and amongst leaf litter.

Remarks

The shell is less depressed than in the majority of other species of Chondrocyclus . The population of C. alabastris at Gamtoos River mouth has similar proportions but the periostracal flanges are serrated. The periostracum of C. herberti sp. nov. is distinctive; the flanges have broadly rounded apices and an unserrated margin. C. convexiusculus also has similar proportions and widely spaced costae, but the shape of the flanges as well as the radulae, distinguish the species. The operculum of C. herberti sp. nov. is more concave than that of C. alabastris and lacks the furrow between the vertical portion of lamellar blade and fringe.

Chondrocyclus herberti sp. nov. is known only from the narrow valley of the Baviaanskloof, in isolated patches of relatively dry thicket and in thicket/fynbos transitional areas. C. herberti sp. nov. and C. alabastris have not been recorded sympatrically, although they occur in steep-sided river valleys in close proximity to each other (Fig. 9). Both of these valleys are tributaries of the Gamtoos River, a postulated dispersal corridor between the coast and the Baviaanskloof (Geldenhuys 1997). Watersheds may have been significant barriers to gene flow for thicket plant and insect species during glacial periods as thicket retracted downward into catchment valleys and survived in isolated refugia (Price et al. 2010; Potts et al. 2012). Terrestrial fauna with poor dispersal ability were also bounded by watersheds during Pleistocene climate cycling (Herbert & Moussalli 2010).

When the animals were killed by drowning, they survived for a couple of weeks fully submerged with head and foot extended, which although not quantified, was longer than any other species. Chondrocyclus herberti sp. nov. can be very abundant; D. Herbert (pers. comm.) who first collected the species at Poortjies, found in excess of 1000 shells per m 2 in a leaf litter sample.