Chondrocyclus convexiusculus ( Pfeiffer, 1855 )

Cole, Mary L., 2019, Revision of Chondrocyclus s. l. (Mollusca: Cyclophoridae), with description of a new genus and twelve new species, European Journal of Taxonomy 569, pp. 1-92 : 9-12

Chondrocyclus convexiusculus ( Pfeiffer, 1855)

Figs 4 , 5 , 8C

Cyclostoma (Cyclophorus) convexiusculum Pfeiffer, 1855: 104 (type loc.: Simonstown [Macgillivray]).

Cyclophorus convexiusculus var. minor Benson, 1856: 438 (type loc.: Table Mountain [Layard]).

Chondrocyclus convexiusculus – Kobelt 1902: 230 . — Connolly 1939: 536. — Herbert & Kilburn 2004: 92.

Diagnosis

Shell small, depressed, lenticular; protoconch mammillate and tilted; periostracum with axial costae developing at the periphery broad triangular flanges each terminating in a long, hair-like spine; operculum flattened, exterior portion shallowly concave, with step-shaped multispiral lamella terminating in a long solid fringe; radula with three large cusps on second lateral tooth.

Etymology

The specific name is derived from the Latin ‘ convex ’, meaning ‘arched or vaulted’.

Type material examined

Syntypes

SOUTH AFRICA – Western Cape • 3 specimens; syntypes of Cyclostoma (Cyclophorus) convexiusculum Pfeiffer, 1855 ( Fig. 4A ); Simons Bay ; [Mrs] Cuming leg.; NHMUK 20120231 .

Other material examined

SOUTH AFRICA – Western Cape • 6 specimens; Cape Peninsula, Simonstown ; 34.1912° S, 18.4211°E; M. Connolly coll.; NMSA 2777 • 2 specimens; same collection data as for preceding; ex. M. Connolly coll.; NMSA A8004 • 11 specimens; Cape Town, 2.8 km south of Miller’s Point, forest in a depression with a few invasive trees ( Eucalyptus and Port Jackson ), steep slope with rocks and root buttresses; 34.2507° S, 18.4729° E; 25 Jun. 2011; R. Daniels leg.; thick and moist leaf litter, about a week of rain before collection; ELM D16879 • 11 specimens; same collection data as for preceding; ELM W3636 • 1 specimen in ethanol; same collection data as for preceding; NHMUK 20120276 • 40 specimens; same collection data as for preceding; 1 Feb. 2012; R. Daniels leg.; ELM D16880 • 17 specimens; same collection data as for preceding; ELM W3637 • 3 specimens; same collection data as for preceding; NHMUK 20120277 • 2 specimens; same collection data as for preceding; NMW.Z.2012.065.00007 • 5 specimens; DuToits Kloof, Donkerkloof, patch of Southern Afrotemperate forest in steep ravine; 33.7536° S, 19.0696° E; 462 m a.s.l.; 7 Aug. 2014; M. Cole leg.; ELM D17970 • 1 specimen; same collection data as for preceding; ELM W3891 • 26 specimens; Kogelberg Nature Reserve, small patch of Southern Afrotemperate forest near Leopards Gorge waterfall; 34.3409° S, 18.9407°E; 312 m a.s.l.; 12 Aug. 2014; M. Cole leg.; ELM D17955 • 22 specimens; same collection data as for preceding; ELM W03876 • 22 specimens; Kogelberg Nature Reserve, Oudebosch, patch of Southern Afrotemperate forest in kloof with Oudebos River ; 34.3337° S, 18.9487°E; 260 m a.s.l.; 12 Aug. 2014; M. Cole leg.; ELM D17975 • 25 specimens; same collection data as for preceding; ELM W03877 .

Description

SHELL ( Fig. 4 B–D). Small, depressed, lenticular, adult diameter 3.97–5.18 mm, height 2.29–3.20 mm, diameter:height 1.59–1.88 (n = 21). Spire little exserted, apex mammillate and tilted ( Fig. 4A, C ). Embryonic shell ( Fig. 4E ) approx. 2.25 whorls, microscopically malleate, sculpture strongest on earliest part, junction between embryonic shell and teleoconch evident with development of axial costae and threads on teleoconch. Teleoconch comprising 2.25 whorls, convex, rapidly increasing, suture deeply impressed. Aperture circular, last whorl descending near aperture, peristome simple, continuous and free. Umbilicus wide and deep, exposing all the whorls. Periostracum glossy, honey-brown and lacquerlike with lamellate axial costae at regular intervals, 44–61 (n = 16) on last whorl, developing at periphery broad triangular flanges terminating in a long, hair-like spine ( Figs 4F , 8C ); intervals between costae with 3–5 indistinct microscopic axial threads. Shell translucent glossy honey-brown or creamy-white when fresh.

LIVING ANIMAL. Head, tentacles and snout dark grey; underside of foot white.

OPERCULUM ( Fig. 4 H–I). Duplex, outer portion concave, consists of multispiral lamella with almost five whorls, each step-shaped; the growing edge of the lamellar blade angular and is more or less perpendicular to disc where it is attached; long fringe of fused bristles emanates from outer side of lamellar blade and curves upwards and outwards forming a furrow between fringe and lamellar blade partially covered by top edge of lamellar blade which curves outwards; top edge of lamella projects above fringe; fringe of each whorl fused to lamella of following whorl.

RADULA ( Fig. 4G ). Rachidian with five cusps, central cusp approx. twice as long as two on either side of it; first and second lateral tooth each with four cusps and a swelling representing the fifth cusp, first three cusps (from centre) increasing in size and fourth considerably smaller.

PENIS ( Fig. 4 J–K). Shaft more-or-less cyclindrical with slightly swollen distal end and a short intromittent organ.

Distribution and habitat

Western Cape, mountains of the Cape Peninsula and north-south running mountains to the east of the Cape Flats. Inland populations appear to be bounded by the upper Breede River valley and coastal populations by the relatively low-lying Agulhas Plain ( Fig. 5 ). There are no records from the Riviersonderend Mountains.

Western Cape Afrotemperate forest ( von Maltitz et al. 2003), very small patches in sheltered ravines; in leaf-litter.

Remarks

Connolly (1929) distinguished this species from C. alabastris on the basis of the second lateral tooth of the radula, that of C. convexiusculus having three large cusps and C. alabastris two. This is confirmed by comparing Fig. 4G and Fig. 7F . There are also differences in the periostracum and operculum discussed under C. alabastris . The molecular analyses placed C. convexiusculus and C. alabastris in different clades ( Fig. 1 ).

Figures

Fig. 4. Chondrocyclus convexiusculus (Pfeiffer, 1855). A. Syntype (NHMUK 20120231). B–K. ELM W3636. B. Dorsal view. C. Aperture view. D. Ventral view. E. Protoconch. F. Detail of axial lamellae of periostracum. G. Portion of radula. H–I. Operculum. J–K. Penis, lateral and dorsal views, showing position on head. Scale bars: A, C = 3 mm; B, D = 2 mm; E = 200 µm; F, J–K = 500 µm; G = 50 µm; H–I = 1 mm.

Fig. 5. Distribution map of the two major clades in the Western Cape province, the Southwestern Cape clade (purple) and the Overberg clade (orange). T indicates type localities.

Fig. 8. Close-up of periostracum of species of the Southern-Eastern Cape clade and Chondrocyclus convexiusculus (Pfeiffer, 1855), showing variation in detail of flanges at periphery. A. C. alabastris (Craven, 1880) (serratededge typical) (ELMW3640). B. C. alabastris, Grahamstownarea (ELMW3690). C. C. convexiusculus (ELM W3636). D. C. herberti sp. nov. (ELM W3691). Scale bar = 500 µm.

Fig. 7. Chondrocyclus alabastris (Craven, 1880). A. Protoconch (ELM D16888). B. Detail of axial lamellae of periostracum (ELM W3639). C–E. Operculum (ELM W3640). F. Portion of radula (ELM W3640). G. Penis, lateral view, showing position (ELM W3638). H. Penis, dorsal view (ELM W3642). Scale bars: A = 200 µm; B, G–H = 1 mm; C–E = 500 µm; F = 50 µm.

Fig. 1. Bayesian Inference majority consensus tree of the “taxa complete” concatenated CO1-16S sequence dataset for Chondrocyclus s.l. Ancey, 1898 (84 sequences) and seven other caenogastropods with the tree rooted on Pomacea insularum (d’Orbigny, 1837) (modified from Cole et al. 2019). Colours indicate major clades of Chondrocyclus Ancey, 1898 and correspond with colours used in maps. Support values are given as posterior probabilities for Bayesian analysis above nodes (only values ≥ 0.95 are shown) and as bootstrap percentages for ML analysis below nodes (only values ≥ 65% are shown); maximal support (Bayesian = 1, ML = 100%) is indicated by an asterisk. Scale bar indicates substitutions per site.