Chondrocyclus silvicolus, Cole, 2019
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Chondrocyclus silvicolus sp. nov.
Shell small, moderately depressed; protoconch mammillate and tilted; periostracum with widely spaced axial costae developing at the periphery broad flanges with pointed tips, tips are rounded not spinetipped; 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.
The specific name is derived from the Latin ‘ silvicolus ’, meaning ‘an inhabitant of the woods’ and referring to the occurrence of the species in the largest forest blocks in South Africa, in the Knysna area.
Type material examined
SOUTH AFRICA – Western Cape • Knysna Forest, Garden Route National Park, Diepwalle ; 33.95° S, 23.15°E; 28 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; NMSA P0639 View Materials /T4156. ( Fig. 10C, F View Fig ) GoogleMaps
SOUTH AFRICA – Western Cape • 1 specimen; same collection data as for holotype; ELM D16892 View Materials / T45 GoogleMaps • 4 specimens; same collection data as for holotype; ELM W3644 View Materials /T46 GoogleMaps • 1 specimen; Knysna Forest, Diepwalle, Ysterhoutrug ; 33.9506°S, 23.1496°E; 28 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16963 View Materials /T45 GoogleMaps • 4 specimens; same collection data as for preceding; NHMUK20160073 View Materials GoogleMaps • 3specimens; same collection data as for preceding; NMW.Z.2016.003.00001 GoogleMaps • 4 specimens; same collection data as for preceding; RMNH.MOL.338283 GoogleMaps • 3 specimens; Knysna Forest Diepwalle, Ysterhoutrug ; 33.966° S, 23.150°E; 28 Apr. 1997; D. Herbert leg.; sorted from leaf-litter; NMSA V4710 View Materials /T4126 GoogleMaps • 1 specimen; Knysna Forest, Diepwalle, vicinity of King Edward VII Big Tree ; 33.9562°S, 23.1521°E; 28 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16962 View Materials /T53 GoogleMaps • 17 specimens; Tsitsikamma Forest, near Paul Sauer Bridge ; 33.950°S, 23.933°E, 28 Apr. 1997; D. Herbert leg.; sorted from leaf-litter; NMSA V4730 View Materials /T4125 GoogleMaps • 31 specimens; Tsitsikama Forest, near Paul Sauer bridge over Storms River , 33.9674° S, 23.9293° E; 27 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16893 View Materials /T52 GoogleMaps • 1 dry specimen; same collection data as for preceding; NHMUK 20160074 View Materials GoogleMaps • 1 specimen in ethanol; same collection data as for preceding; NHMUK 20160075 View Materials GoogleMaps • 1 specimen; same collection data as for preceding GoogleMaps ;
RMNH.MOL338284 • 14 specimens; same collection data as for preceding; ELM W3645 View Materials /T51 • 12 specimens; Goukamma N.R., 10 km west of Knysna , banks of Goukamma River 2.7 km upstream of mouth, riverine forest below River Lodge; 34.0591°S, 22.9389° E; 12 Mar. 2015; M. Cole leg.; ELM D17939 View Materials /T47 GoogleMaps • 4 specimens; same collection data as for preceding; ELM W 3869 View Materials /T48 GoogleMaps • 10 specimens; Wilderness National Park , trail along west bank of Touw River opposite Ebb and Flow North campsite; 33.9843° S, 22.6073°E; 12 Mar. 2015; M. Cole leg.; ELM D17946 View Materials /T50 GoogleMaps • 1 specimen; same collection data as for preceding; ELM W3871 View Materials /T49 GoogleMaps .
Other material examined
SOUTH AFRICA – Western Cape • 1 specimen; Tsitsikama Forest, near Paul Sauer bridge over Storms River ; 33.9674° S, 23.9293°E; 16 Aug. 2014; M. Cole leg.; ELM D17972 View Materials GoogleMaps • 2 specimens; Natures Valley, Kalanderkloof Trail, opposite Devasselot Restcamp , east-facing rocky slope; 33.971°S, 23.558° E; 27 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16997 View Materials GoogleMaps • 4 specimens; Natures Valley, North side of Groot River , near Devasselot Restcamp ; 33.966° S, 23.563° E; 27 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16894 View Materials GoogleMaps • 1 specimen; Knysna Forest, Diepwalle, Velsbroekdraai ; 33.9382° S, 23.1574° E; 28 Jan. 2011; M. Cole, V. Ndibo and R. Daniels leg.; ELM D16964 View Materials GoogleMaps • 1 specimen; Goukamma Nature Reserve, 10 km west of Knysna, on banks of Goukamma River , 2.3 km upstream of mouth, riverine forest behind Forest Lodge ; 34.0614° S, 22.9396° E; 12 Mar. 2015; M. Cole leg.; ELM D17959 View Materials GoogleMaps • 4 specimens; Goukamma Nature Reserve, 10 km west of Knysna, on banks of Goukamma River , 2.3 km upstream of mouth, riverine forest behind Forest Lodge ; 34.0614° S, 22.9396° E; 15 Mar. 2014; M. Cole leg.; ELM D17965 View Materials GoogleMaps .
SHELL ( Fig. 13 View Fig A–C). Small, moderately depressed, adult diameter 3.76–6.10 mm, height 2.09–3.84 mm, diameter:height 1.5–1.97 (n = 49). Spire moderately exserted, protoconch mammillate and tilted. Embryonic shell ( Fig. 13D View Fig ) approx. 2.5 whorls, microscopically malleate, junction between embryonic shell and teleoconch evident with development of costae on teleoconch. 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 wide and deep, exposing all the whorls. Periostracum glossy, light yellowish-brown and lacquer-like with relatively widely spaced ridged, lamellate axial costae at regular intervals, 59–79 (n = 13) on last whorl, which produce broad, pointed flanges with rounded tips at periphery ( Fig. 13E View Fig ); intervals between costae with six to nine distinct microscopic axial threads. Shell translucent golden brown or creamy white when fresh.
LIVING ANIMAL. Head, tentacles and snout pigmented with grey; underside of foot creamy white.
OPERCULUM ( Fig. 13 View Fig G–H). Duplex, outer portion shallowly concave and consisting of multispiral lamella with 4.75 whorls, each step-shaped and increasing in height towards outside, sloping at growing edge; 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. 13F View Fig ). Rachidian with five cusps, central one approx. twice length of outer two on each side; first lateral tooth with three large cusps, one small 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. 13I View Fig ). Shaft more or less cylindrical, intromittent organ short.
Distribution and habitat
Western Cape, from Storms River to Wilderness (Touw River) ( Fig. 9 View Fig ). Indigenous Southern Cape Afrotemperate Forest and Western Cape Milkwood Forest ( von Maltitz et al. 2003); in leaf-litter.
The shell is less depressed than in the majority of other species of Chondrocyclus . Chondrocyclu. herberti sp. nov. has similar proportions, but the costae in C. silvicolus sp. nov. are not as widely spaced ( Table 2) and have more pointed ends. C. silvicolus sp. nov. shells are also larger on average ( Table 2). The two species inhabit different environmental conditions. C. silvicolus sp. nov. is a species of the ancient Southern Cape Afrotemperate forests, while C. herberti sp. nov. is adapted to drier conditions. Forest patches between the Baviaanskloof with C. herberti sp. nov. and the Southern Cape Afrotemperate forests where C. silvicolus sp. nov. occurs, have not been sampled.
Chondrocyclus convexiusculus has similar proportions and relatively widely spaced costae, but the ends of the flanges are produced into a narrow point. The operculum is less concave and the radula differs in having three rather than two large cusps on the second lateral tooth.
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