Chondrocyclus kevincolei, Cole, 2019

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 : 56-61

Chondrocyclus kevincolei sp. nov.

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Figs 5 , 10 P–Q, 26

Chondrocyclus convexiusculus – Connolly 1939: 537 .

Diagnosis

Shell small, depressed, lenticular; periostracum with axial costae producing spiral rows of simple hairs; spiral grooves on shell corresponding with rows of hairs; operculum duplex, exterior portion very shallowly concave, with step-shaped multispiral lamella terminating in a short fringe with uneven edge, diameter of exterior portion less than diameter of inner disc; radula with three large cusps on second lateral tooth.

Etymology

Named for the author’s husband, Kevin Cole, in acknowledgement of his indispensable assistance on fieldtrips.

Type material examined

Holotype

SOUTH AFRICA – Western Cape • Platbos Forest near Gansbaai, Western Cape Milkwood Forest with large trees including Sideroxylon inerme Linne and Celtis africana N.L. Burm ; 34.5671°S, 19.4495°E; 13 Aug. 2014; M. and K. Cole leg.; in leaf litter; NMSA W9270/T3073 . ( Fig. 10 P–Q)

Paratypes

SOUTH AFRICA – Western Cape • 1 specimen; same collection data as for holotype; ELM D18004/ T 85 • 2 specimens; same collection data as for holotype; ELM W 3898 / T 86 • 327 specimens; same collection data as for preceding; 9 Sep. 2009; M. Cole, K. Cole, D-J Hodgkinson and T. Pretorius leg.; ELM D16921/ T 81 • 90 specimens; same collection data as for preceding; ELM W 3615 / T 82 • 20 specimens; same collection data as for preceding; NHMUK 20120282 • 23 specimens; same collection data as for preceding; NMSA P 0598 / T 4121 • 18 specimens; same collection data as for preceding; NMW. Z.2012.065.00010 • 15 specimens; same collection data as for preceding; RMNH MOL.330503 • 47 specimens; same collection data as for preceding; 18 Apr. 2012; M. Cole, D. Herbert and L. Davis leg.; ELM D16998/ T 83 • 5 specimens; same collection data as for preceding; ELM W 3659 / T 84 • 27 specimens; Bredasdorp, about 5 miles to SW, on Elim Rd ; 34.5450° S, 19.9614° E; ex Transvaal Museum; dry bush on hillside; NMSA W 575 / T 4123 • 34 specimens; Bredasdorp, 7 km south west on R 43 to Elim , bushy valley with dam; 34.5912° S, 19.9992° E; 35 m a.s.l.; 13 Aug. 2014; M. Cole leg.; ELM D17983/ T 87 • 15 specimens; same collection data as for preceding; ELM W 3890 / T 88 • 23 specimens; Grootbos Nat. Res., Gansbaai area, Milkwood forest ; 34.5421° S, 19.4153° E; 7 Oct. 2007; D. Herbert and L. Davis leg.; in leaf-litter; NMSA W 5659 / T 4122 • 45 specimens; Grootbos Private Nature Reserve, between Stanford and Gansbaai, Western Cape Milkwood Forest ; 34.5419° S, 19.4122° E; 203 m a.s.l; 13 Aug. 2014; M. Cole leg.; D18005/ T 89 • 6 specimens; Gansbaai dune scrub; 34.5795° S, 19.3442° E; 13 Feb. 2005; A. Moussalli and D. Stuart-Fox leg.; in leaf-litter; NMSA W 3537 / T 4124 .

Description

SHELL ( Fig. 26 A–F). Small, depressed, lenticular, adult diameter 3.59–5.34 mm, height 1.59–2.84 mm, diameter:height 1.68–2.37 (n = 87 from 4 populations; variations in dimensions between populations are given in Table 4 ). Spire little exserted, protoconch large and mammillate ( Fig. 26A ). Embryonic shell ( Fig. 26G ) approx. 2.25 whorls, almost smooth but microscopically malleate at tip, junction between embryonic shell and teleoconch evident with development of costae on teleoconch. Teleoconch comprising just over two whorls, very 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 Fig. 26C, F ). Periostracum glossy and lacquer-like with lamellate axial costae at regular intervals on last whorl, 51–75 (n = 22) in Platbos population, but vary between populations ( Table 4 ), which produce spiral rows of simple hairs varying in different populations from approx. 4–14 on last whorl, longest at periphery and shortest around umbilicus; intervals between axial costae with approx. eight microscopic axial threads ( Fig. 26H ); shell bears spiral grooves corresponding with the rows of hairs ( Fig. 26 D–F). Shell translucent when fresh; two colour morphs present reddish brown and creamy white.

LIVING ANIMAL. Varies in colour between populations from creamy white with slight pigmentation on tentacles to very dark grey (see below).

OPERCULUM ( Fig. 26 J–K). Duplex, shallowly concave; multispiral lamella of outer portion with 4.5 whorls, each step-shaped, growing edge of lamella at angle, perpendicular where it is attached to disc; fringe very short and solid, with a frayed distal edge even in fresh specimens, fringe of each whorl not fused to lamellar blade of following whorl, diameter of outer multispiral portion smaller than diameter of inner disc due to very short fringe; operculum retractile.

RADULA ( Fig. 26I ). Rachidian with five cusps, middle one longer than two cusps on either side of it; first and second lateral teeth each with four cusps and a vestigial 5 th, the third cusp from centre the largest.

PENIS ( Fig. 26L ). Shaft more or less cylindrical and slightly flattened dorsoventrally, distal half slightly expanded on left side, numerous annular rugae, distal end smooth, intromittent organ short.

Distribution and habitat

Western Cape, Agulhas Plain, between Gansbaai and Bredasdorp. Various forested or bushy habitats in patches of Western Cape Milkwood Forest (part of Southern Coastal forest group) ( von Maltitz et al. 2003) with large trees, characterised by white milkwoods ( Sideroxylon inerme ), white stinkwoods ( Celtis africana ) and white pear ( Apodytes dimidiata E. Mey. ex Arn. ), including the southernmost forests in Africa (Platbos and Grootbos), dune scrub at Gansbaai and ‘dry bush on hillside’ (south-west of Bredasdorp); in leaf-litter ( Fig. 5 ).

Remarks

The distinct spiral grooves on the shell of C. kevincolei sp. nov. ( Fig. 26 D–F) are unique among species of Chondrocyclus although there are sometimes faint traces of spiral grooves on shells of A. isipingoensis gen. et comb. nov. and C. langebergensis sp. nov. visible only at very high magnification. Chondrocyclus langebergensis sp. nov. differs from C. kevincolei sp. nov. in its lack of prominent spiral grooves on the shell, the spiral rows of long hairs are concentrated around the periphery, the protoconch is more strongly sculptured and the opercula differ. In C. langebergensis sp. nov., the lamellar fringe of each spiral whorl of the operculum emanates from a ridge at the base of the lamellar blade and is fused to the lamellar blade of the following whorl. The terminal fringe is long and overlaps the base when viewed from above ( Fig. 25F ). In C. kevincolei sp. nov. the fringe emanates from near the top of the lamellar blade and is very short and appears distinct from the following lamellar whorl; the outer saucershaped portion is smaller than the polished base ( Fig. 26J ). These differences together with molecular evidence, are considered to warrant recognition of at least two distinct species, one in the Langeberg Mountains and the other on the relatively low-lying coastal region of the Agulhas Plain. The Langeberge and Agulhas Plain are separated by the Breede River valley and by a belt of relatively arid vegetation, consisting mainly of Ruens Shale Renosterveld and Agulhas Limestone Fynbos ( Rebelo et al. 2006), which developed in the Pliocene ( Cowling et al. 2008). Molecular studies in unrelated faunal taxa also provide evidence for separate lineages in the Langeberge and the Agulhas Plain (e.g., Price et al. 2007; Moussalli et al. 2009; Gouws et al. 2010; McDonald & Daniels 2012) and for an absence of gene flow between these areas ( Myburgh & Daniels 2015). Species of Chondrocyclus have not been recorded in the Riviersonderendberge where apparently suitable habitat exists.

There are morphological differences between populations of C. kevincolei sp. nov. ( Table 4 ). The number of spiral rows of hairs is fewer in the Bredasdorp population (only 4–5 as opposed to 8–15 in the Platbos and Grootbos populations). The colour of the living animal is creamy white with only slight pigmentation of the tentacles in the Platbos population and dark grey to almost black at Bredasdorp. There were relatively large genetic divergences between populations ( Cole et al. 2019). Their long branch lengths ( Fig. 1 ) suggest isolation in shrinking refuges as arid-adapted vegetation replaced forest (see Tolley et al. 2006, 2008). Recent radiations of faunal taxa in this region are associated with adaptation to open habitats ( Tolley et al. 2006; Herbert & Moussalli 2010). Sea level changes have also had dramatic effects on vegetation of the Agulhas Plain ( Linder 2003) and its biota with marine transgressions potentially restricting ancestral populations of Chondrocyclus to refuges at higher elevations and thus driving allopatric divergence or eliminating closely related taxa at lower elevations. Further studies including unsampled populations on the Agulhas Plain and additional markers may shed light on whether separate populations may warrant species status. It was, however, decided to treat these as one species pending further investigation. By contrast, C. langebergensis sp. nov. occurs in relatively stable relictual forest patches in the Langeberge and has undergone little change.

Genus Afrocyclus gen. nov.

urn:lsid:zoobank.org:act:0C542886-FB1A-4550-BBC2-80BBD28FA01E

Type species

Afrocyclus isipingoensis ( Sturany, 1898) gen. et comb. nov.

Diagnosis

Shell dextral, small, depressed; aperture circular, last whorl descending near aperture, peristome not thickened, continuous and free; umbilicus wide and deep, exposing all the whorls; periostracum glossy and lacquer-like with lamellate axial costae at regular intervals, usually expanded into spiral rows of hairs; operculum duplex, corneous; inner portion consists of a thin disc which grows outwards in a tight spiral, smooth on inside where it attaches to foot; fused to disc on its outer surface is a multispiral, elevated horny blade-like lamella formed by fused bristles; a fringe of fused bristles emanates from outer surface of each lamellar whorl; radula taenioglossate, two large cusps on second lateral tooth; penis lies dorsally immediately behind right tentacle and consists of a stout, muscular, cylindrical shaft, wrinkled along most of its length due to annular rugae, and a terminal, tapering intromittent organ without flagellum; seminal tube completely enclosed without seminal groove.

Etymology

The specific name is derived from ‘Africa’ and refers to its Afromontane occurrence.

Remarks

mtDNA data clarified that Afrocyclus gen. nov. constituted a radiation distinct from that of Chondrocyclus s.s. ( Cole et al. 2019). Specimens of Afrocyclus gen. nov. can in most cases be recognised at a glance on morphological grounds, being very small, very depressed (the apex can even be concave), discoid shells with spiral rows of hairs projecting from the axial costae. This morphotype is widely distributed in latitude and altitude, occupying isolated Afromontane forest patches along the Great Escarpment from northern South Africa (Limpopo province, 23° S) to the Eastern Cape (32.7°S) and extending to the coast ( Fig. 2 ). mtDNA data showed that what was previously lumped as Afrocyclus isipingoensis gen. et comb. nov. is a species complex, and within it, external morphology is relatively conserved, making it difficult to distinguish taxa by morphology alone. A. exsertus gen. et comb. nov., which occupies a narrow zone on the east coast, is strikingly different morphologically, bearing no hairs and with the axial lamellae only slightly expanded around the periphery. The operculum of the latter also deviates dramatically from the flat, fragile operculum of most specimens of Afrocyclus gen. nov. and is more robust with a rigid fringe consisting of bunches of short bristles. Phylogenetic relationships within Afrocyclus gen. nov. are not fully resolved and further molecular and morphological data from throughout its range are required to revise this complex.

Key to species of Afrocyclus gen. nov.

1. Axial lamellae slightly expanded at periphery, but not produced into hairs........................................ ............................................................... A. exsertus ( Melvill & Ponsonby, 1903) gen. et comb. nov.

– Axial lamellae expanded into multiple spiral rows of hairs .............................................................. 2

2. Spiral rows of periostracal hairs include a row of very short hairs immediately below suture on body whorl .................................................................. A. isipingoensis ( Sturany, 1898) gen. et comb. nov.

– No spiral row of very short periostracal hairs immediately below suture......................................... 3

3. Three spiral rows of hairs at periphery; upper edge of rachidian tooth smooth .................................. .................................................................................................................. A. oxygala gen. et sp. nov.

– More than three spiral rows of hairs on body whorl; upper edge of rachidian tooth serrated........... 4

4. Protoconch strongly malleate ...................................................................... A. potteri gen. et sp. nov. – Protoconch malleate, but not strongly .......................................................... A. bhaca gen. et sp. nov.

Figures

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. 10. Holotypes of species of Chondrocyclus Ancey, 1898. A–B. C. herberti sp. nov., diameter 3.70 mm (NMSA P1043/T4277). C, F. C. silvicolus sp. nov., diameter 5.82 mm (NMSA P0639/T4156). D–E. C. amathole sp. nov., diameter 6.01 mm (NMSA P0640/T4157). G–H. C. pondoensis sp. nov., diameter 5.92 mm (NMSA P0643/T4160). I, L. C. devilliersi sp. nov., diameter 5.23 mm (NMSA P1141/ T4312). J–K. C. pulcherrimus sp. nov., diameter 4.34 mm (NMSA W9272/T3075). M–N. C. cooperae sp. nov., diameter 4.93 mm (NMSA W9271/T3074). O, R. C. langebergensis sp. nov., diameter 5.13 mm (NMSA P0642/T4159). P–Q. C. kevincolei sp. nov., diameter 4.24 mm (NMSA P9270/T3073).

Fig. 26. Chondrocyclus kevincolei sp. nov. A. Aperture view (ELM W3615/T82). B. Dorsal view (ELM W3615/T82). C. Ventral view (ELM W3615/T82). D–F. Shell views, showing spiral grooves (NMSA W5659/T4122). G. Protoconch (ELM W3615/T82). H. Detail of axial lamellae of periostracum (ELM W3615/T82). F. Portion of radula (ELM W3615/T82). J–K. Operculum (ELM W3615/T82). L. Penis, lateral view (ELM W3615/T82). Scale bars: A–F = 2 mm; G = 200 µm; H, J–K = 500 µm; I = 50 µm; L = 1 mm.

Fig. 25. Chondrocyclus langebergensis sp. nov. A. Aperture view (NMSA W1043/T4117). B. Dorsal view (NMSA W5008/T4119). C. Ventral view (NMSA W5008/T4119). D. Protoconch (ELM W3614/ T96). E. Portion of radula (NMSA W5008/T4119). F. Operculum, dorsal view (ELM W3614/T96). G. Penis, dorsal view showing position behind right tentacle (ELM W3660/T91). H. Penis, lateral view (NMSA W5008/T4119). I. Operculum, lateral view (NMSA W5008/T4119). Scale bars: A–C = 2 mm; D = 200 µm; E = 50 µm; F, I = 500 µm; G–H = 1 mm.

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.

Fig. 2. Map of South Africa showing distribution of the five major clades of Chondrocyclus s.l. Ancey, 1898. Provinces with records of Chondrocyclus are labelled.