Chondrocyclus alabastris ( Craven, 1880 )

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 : 12-18

Chondrocyclus alabastris ( Craven, 1880)

Figs 6–7 , 8 A–B, 9

Cyclotus alabastris Craven, 1880: 619 (type loc.: Cape Recif, Algoa Bay [Craven]).

Cyclophorus (Maizania) alabastris – Kobelt 1902: 149 .

Chondrocyclus alabastris – Connolly 1929: 238 ; 1939: 539.

Diagnosis

Shell small, very depressed, lenticular; protoconch mammillate and tilted; periostracum with axial costae developing at the periphery elongated triangular flanges usually with serrated edges; operculum flattened, exterior portion shallowly concave, with step-shaped multispiral lamella terminating in solid fringe reflexed over peristome; radula with two large cusps on second lateral tooth.

Etymology

From ‘alabaster’, an almost transparent white stone. In his description Craven (1880) describes the species as “semitransparent, of a pure white colour”.

Type material examined

Syntypes

SOUTH AFRICA – Eastern Cape • 7 specimens; syntypes of Cyclotus alabastris Craven, 1880 ; Cape Colony, Algoa Bay , Cape Recif; A.E. Craven leg.; on Sand-Hills; 27 Feb. 1875; NHMUK 1891.3.7.42- 47. ( Fig. 6A )

Other material examined

SOUTH AFRICA – Eastern Cape • 8 specimens; Port Elizabeth, The Island Nature Reserve, indigenous Southern Coastal forest in south facing valley; 33.9867°S, 25.3715°E; 18 Sep. 2008; M. Cole leg.; ELM D15931 • 36 specimens; same collection data as for preceding; 27 May 2011; M. Cole leg.; ELM D16885 • 7 specimens; same collection data as for preceding; ELM W03640 • 3 specimens; same collection data as for preceding; NHMUK 20120270 • 2 specimens; same collection data as for preceding; NMW.Z.2012.065.00003 • 1 specimen; Port Elizabeth, Settlers Park , indigenous riverine forest; 33.9703° S, 25.6123°E; 16 Mar. 2005; A. Moussalli and D. Stuart-Fox leg.; in leaf-litter; NMSA W4602 • 5 specimens; Van Stadens River gorge, west of Port Elizabeth , tall forest on steep slope with stream running down to river; 33.9120°S, 25.2051°E; 22 Sep. 2008; M. Cole leg.; ELM D15969 • 16 specimens; same collection data as for preceding; 27 Sep. 2011; M. Cole leg.; ELM D16882 • 2 specimens; same collection data as for preceding; ELM W03638 • 3 specimens; Loerie Restcamp, near PPC quarry; 33.7971°S, 24.9654°E; 22 Sep. 2008; M. Cole leg.; ELM D15924 • 24 specimens; Maitland Nature Reserve , 2 km from mouth on east side of river, forest on steep slope; 33.9774°S, 25.3121°E; 26 Sep. 2011; M. Cole, D. Herbert and L. Davis leg.; ELM D16881 • 2 specimens; Ningi, (formerly Yellowwoods Farm), on west side of Maitland River 4.5 km upstream of mouth, riverine forest with large Yellowwoods ; 33.9304° S; 25.2083° E; 27 Sep. 2011; M. Cole, D. Herbert and L. Davis leg.; ELM D16883 • 13 specimens; Ferndale, Patensie, Ratelkloof , valley of Noaga River ; 33.7164°S, 24.8503°E; 28 Sep. 2011; M. Cole, D. Herbert and L. Davis leg.; ELM D16884 • 5 specimens; same collection data as for preceding; ELM W03639 • 53 specimens; Gamtoos River mouth, dune forest east of mouth; 33.9574° S, 25.0477°E; 40 m a.s.l.; 28 Sep. 2011; M. Cole, D. Herbert and L. Davis leg.; ELM D16886 • 8 specimens; same collection data as for preceding; ELM W03641 • 1 specimen; Kap River , north bank, indigenous riverine forest on shady, south-facing slope; 33.4830°S, 27.0807° E; 30 m a.s.l.; 13 May 2011; M. Cole leg.; ELM D16887 • 1 specimen; same collection data as for preceding; 30 Dec. 2002; M. Cole leg.; ELM W03026 • 34 specimens; Olifantskop, Southern Mistbelt forest ; 33.3173° S, 26.4991°E; 9 Sep. 2011; M. Cole, D. Herbert and L. Davis leg.; ELM D16890 • 8 specimens; same collection data as for preceding; ELM W03643 • 4 specimens; Van Stadens Pass , bottom of pass, west side of river, steep south facing slope; 33.9095°S, 25.1905°E; 16 Nov. 2012; M. and K. Cole, D. Herbert and L. Davis leg.; ELM D17016 • 4 specimens; Van Stadens Pass , near top of pass, steep north-facing slope; 33.9131° S, 25.2047° E; 163 m a.s.l.; 16 Nov. 2012; M. Cole leg.; ELM D17222 • 9 specimens; Berg River crossing, east bank, 9 km E of Loerie, 7.5 km N.W. of Van Stadens bridge; 33.8746°S, 25.1195°E; 17 Nov. 2012; M. and K. Cole, D. Herbert and L. Davis leg.; ELM D17026 • 6 specimens; same collection data as for preceding; ELM W03668 • 48 specimens; Stinkhoutkloof, 11 km N. E of Loerie, 15 km N.W. of Van Stadens ; 33.7993°S, 25.0967°E; 17 Nov. 2012; M. and K. Cole, D. Herbert, L. Davis and Edwards family leg.; ELM D17034 • 6 specimens; Addo National Park, Zuurberg section, forest in valley of river, on 4 hour trail; 33.3403°S, 25.7362°E; 477 m a.s.l.; 19 Nov. 2012; M. and K. Cole leg.; ELM D17045 • 1 specimen; same collection data as for preceding; ELM W03676 • 7 specimens; Port Elizabeth, Lovemore Heights, south facing slope, Southern Coastal forest ; 33.9928°S, 25.5121°E; 278 m a.s.l.; 18 Nov. 2012; M. and K. Cole leg.; ELM D17120 • 1 specimen; same collection data as for preceding; ELM W03733 • 31 specimens; Grahamstown, Mountain Drive , south facing slope; 33.3281° S, 26.5006°E; 10 Mar. 2007; M. Bursey and V. Ndibo leg.; in leaf-litter; ELM D15286 • 36 specimens; same collection data as for preceding; 20 Nov. 2009; M. Cole leg.; ELM D16888 • 18 specimens; same collection data as for preceding; ELM W03642 • 3 specimens; same collection data as for preceding; NHMUK 20120269 • 38 specimens; same collection data as for preceding; 33.3292° S, 26.4991° E; 6 Feb. 2011; R. Daniels leg.; ELM D16889 • 1 specimen; same collection data as for preceding; ELM W3690 • 2 specimens; same collection data as for preceding; NMW.Z.2012.065.00002 • 13 specimens; Grahamstown, Belmont Valley ; 33.3153°S, 26.5861° E; 1978; D. Herbert leg.; NMSA W581 • 7 specimens; Paradise Kloof, 8 km SW of Grahamstown, runs down southwards into upper Howison’s Poort ( Palmiet River ) from the Coldspring Ridge ; 33.3444° S, 26.4466° E; 710 m a.s.l.; 28 Feb. 2013; M. Cole leg.; collected at top of kloof; ELM D17220 • 9 specimens; same collection data as for preceding; ELM W03740 • 5 specimens; Coleridge, near Stones Hill, 8 km SE of Grahamstown, south facing slope, Southern Mistbelt Forest ; 33.3334° S, 26.6156° E; 2 Mar. 2013; M. and S. Cole leg.; ELM D17221 • 2 specimens; same collection data as for preceding; ELM W03741 .

Description

SHELL ( Fig. 6 B–D). Small, usually very depressed, lenticular, adult diameter 3.7–5.32 mm, height 1.92–2.86 mm, diameter:height 1.79–2.28 (n = 20) (from The Island Nature Reserve, Port Elizabeth, close to type locality). Variation in dimensions between populations is given in Table 1 . Spire little exserted, protoconch acutely mammillate and tilted. Embryonic shell ( Fig. 7A ) approx. 2.25 whorls, microscopically malleate, sculpture strongest on earliest part, junction between embryonic shell and teleoconch evident with development of costae on teleoconch. Teleoconch comprising 2.5 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 lacquer-like with lamellate axial costae at regular intervals, 67– 97 on last whorl (average 80; n = 47), their edges scalloped or serrated in the majority of populations ( Fig. 8A ) and expanded into elongated flanges at periphery, flanges smooth with a spine-tip in populations from around Grahamstown ( Fig. 8B ); intervals between costae with 3–6 microscopic axial threads. Shell translucent honey brown when fresh.

LIVING ANIMAL. Dark grey.

OPERCULUM ( Fig. 7 C–E). Duplex outer portion shallowly concave, and consisting of a multispiral lamella with five whorls, at its growing edge the top edge of the lamellar blade is sloping, becoming perpendicular to the disc where it is attached; fringe of fused bristles emanates near top of vertical portion of lamellar blade on its outer surface and curves upwards and outwards forming a shallow furrow between fringe and lamellar blade, a second very short fringe emanates from lower down on the lamellar blade; top edge of lamella does not project above level of fringe; fringe of each whorl fused to lamella of following whorl. Fringe overlaps disc slightly, but operculum can be withdrawn into aperture.

RADULA ( Fig. 7F ). Rachidian with five cusps, central approx. twice as long as two on either side of it; first lateral tooth with four cusps and sometimes a vestigial fifth, first three cusps (from centre) gradually increasing in size and fourth considerably smaller; second lateral tooth with two large cusps and two small cusps towards outside.

PENIS ( Fig. 7 G–H). Shaft more or less straight-sided and slightly flattened, with numerous annular rugae, intromittent organ short.

Distribution and habitat

Endemic to the Eastern Cape, centered around Port Elizabeth and including the Albany district ( Fig. 9 ). Found in a wider variety of vegetation types than other Chondrocyclus species: Algoa Dune Strandveld, Albany Coastal Forest, Southern Mistbelt Forest, Great Fish Thicket ( von Maltitz et al. 2003; Hoare et al. 2006; Mucina et al. 2006); in leaf-litter.

Remarks

There is variation in size of shells between populations ( Table 1 ), an observation also recorded by Connolly (1939). Shells in some populations are among the largest recorded in the genus (the only other species attaining a similar size is C. amathole sp. nov.). However, the types ( Fig. 6A ) from Cape Receife, populations at The Island Nature Reserve (40 km west of type locality) and at Gamtoos River mouth are smaller on average and the population at Gamtoos mouth has a distinctly less depressed shape than is typical for the species. Its diameter/height proportions resemble those of relatively less depressed species, e.g., C. convexiusculus , C. herberti sp. nov. and A. exsertus gen. et comb. nov.

There was a relatively large intraspecific divergence in C. alabastris ( Cole et al. 2019) and the species contained several very well-supported subclades ( Fig. 1 ). There was a distinct lineage in the mistbelt forest patches on the Rietberg ridge south of Grahamstown (Paradise Kloof and Coleridge in Fig. 1 ). This lineage exhibited a conspicuous variation from other populations of C. alabastris : the peripheral extensions of the axial lamellae were not serrated along the edges and each flange tapered gradually into a short spine tip ( Fig. 8B ). Specimens from these localities superficially resembled C. convexiusculus ( Fig. 8C ). However, the spines are longer in C. convexiusculus , emanating from a relatively short, broad triangular proximal portion while in C. alabastris the triangular flanges taper gradually into the short spine tip ( Fig. 8B ).

The lamellar blade of the outer portion of the operculum of C. alabastris is relatively lower and hence the operculum is less concave than that of C. convexiusculus , and has a very short fringe below the long fringe, absent in C. convexiusculus .

Figures

Fig. 6. Chondrocyclus alabastris (Craven, 1880). A. Syntype (NHMUK 1891.3.7.42). B. Aperture view (ELM D16882). C. Dorsal view (ELM W3640). D. Ventral view (ELM W3640). Scale bars: A = 3 mm; B–D = 2 mm.

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. 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. 9. Distribution map of Chondrocyclus species in the Southern-Eastern Cape clade in the southern Cape area of the Western Cape province and the western half of the Eastern Cape province. T indicates type localities. Major cities and rivers are labelled.

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.