Afrocyclus exsertus ( Melvill & Ponsonby, 1903 ) 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 : 75-82

Afrocyclus exsertus ( Melvill & Ponsonby, 1903) gen. et comb. nov.

Figs 29 , 33

Chondrocyclus exsertus Melvill & Ponsonby, 1903: 608 , pl. xxxii, fig. 11 (type loc.: Umkomaas).

Chondrocyclus exsertus – Connolly 1939: 540 . — Herbert & Kilburn 2004: 92.

Diagnosis

Shell very small, moderately depressed; periostracum with dense axial costae increasing slightly in height at periphery but not expanded into spines or flanges; operculum duplex, almost flat, multispiral lamellar blade low, loose fringe of bunches of bristles, fringe of each whorl with free ends not fused to lamella of following whorl; umbilicus deep and widely open exposing all the whorls; radula with two large cusps on second lateral tooth.

Etymology

The specific name is derived from the Latin ‘ exsertus ’, meaning ‘stretched or thrust out’, and referring to the elevated spire.

Type material examined

Holotype

SOUTH AFRICA – KwaZulu-Natal • Umkomaas; J.H. Ponsonby Esq. leg.; NHMUK 1904.4 .29.28. ( Fig. 33A )

Other material examined

SOUTH AFRICA – KwaZulu-Natal • 5 specimens; Kelso junction; NMSA A8011 • 4 specimens; same collection data as for preceding; ex Transvaal Museum; NMSA W465 • 20 specimens; Umzumbe, Trust Farm, 4.3 km inland of Umzumbe as crow flies, small patch of indigenous forest among sugar cane; 30.6100° S, 30.5070°E; 9 Jan. 2012; M. Cole, D. Herbert, L. Davis and D. Kinsler leg.; ELM D16953 • 2 specimens; same collection data as for preceding; ELM W03655 • 2 specimens in ethanol; same collection data as for preceding; NHMUK 20120275 • 4 specimens; Frome Farm, Sunwich Port , 3.8 km inland from coast; 30.6498° S, 30.4786°E; 100 m a.s.l.; 14 Apr. 2011; M. Cole, D. Herbert, L. Davis and R. Daniels leg.; ELM D16951 • 15 specimens; same collection data as for preceding; 8 Jan. 2012; M. Cole, K. Cole and D. Kinsler leg.; ELM D16952 • 3 specimens; same collection data as for preceding; ELM W3654 • 11 specimens; same collection data as for preceding; 21 Jan. 2012; D. Kinsler leg.; ELM D17010 • 2 specimens; same collection data as for preceding; NMW.Z.2012.065.00006 • 12 specimens; same collection data as for preceding; 4 Feb. 2015; D. Kinsler leg.; ELM D17935 • 5 specimens; Umzumbe, Clouds Hill ; 30.6275° S, 30.5308° E; 21 m a.s.l.; 13 Feb. 2012; D. Kinsler leg.; ELM D17011 • 15 specimens; same collection data as for preceding; 4 Feb. 2015; D. Kinsler leg.; ELM D17936 .

Description

SHELL ( Fig. 33 A–C). Very small, adult diameter 2.96–4.64 mm, height 1.82–2.86 mm, diameter:height 1.39–1.86 (n = 25) ( Fig. 33 A–B, E–F). Spire moderately exserted, protoconch not mammillate ( Fig. 33B ). Embryonic shell ( Fig. 33C ) just over 2.5 whorls, microscopically malleate, roughest in centre; junction between embryonic shell and teleoconch evident with development of costae on teleoconch. Teleoconch comprising just under two 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 ( Fig. 33F ). Periostracum pale yellowish-brown with lamellate axial costae at regular intervals, 84–110 (n = 14) on last whorl, each lamellar blade has numerous tiny vertical ridges visible at very high magnification ( Fig. 33D ); lamellar blades increase in height at periphery but not expanded into flanges or hairs; intervals between costae with microscopic axial threads. Shell translucent and corneous when fresh.

OPERCULUM ( Fig. 33H, J ). Duplex, almost flat, multispiral outer portion with a broad, thin nucleus and six whorls, height of lamellar blade low and not stepped, thickened horizontal ridge near bottom of blade just above disc surface, loose fringe of bristles emanates from ridge, fringe consists of bunches of short bristles, with free ends not fused to lamella of following whorl, fringe of outer whorl overlaps disc slightly.

RADULA ( Fig. 33G ). Rachidian with five cusps, central cusp approx. twice length of outer cusps, outermost cusps relatively weak, cusps of rachidian set a little distance below ‘top’ of tooth, top edge serrated; first lateral tooth usually with three large cusps, third cusp (from centre) largest, a small fourth cusp and a vestigial fifth; second lateral tooth with two large cusps, second cusp (from centre) longer and broader than first, a very small third cusp and a vestigial fourth.

PENIS ( Fig. 33I, K ). Shaft short, broad and more or less cylindrical, intromittent organ very short.

Distribution and habitat

Endemic to the coastal belt of southern Kwazulu-Natal and possibly extending into northern Pondoland. Recent specimens found in a few small patches of remaining indigenous forest inland of Umtentwini and Umzumbe ( Fig. 29 ).

Indigenous Scarp Forest ( Mucina & Geldenhuys 2006), on steep, rocky slopes, in leaf litter.

Remarks

The spire is more elevated than in the majority of other species of Afrocyclus and in the majority of species of Chondrocyclus s.s. barring C. herberti sp. nov., with similar shell proportions to the latter. The periostracum has simpler axial lamellae than other species, lacking flanges or hairs. The operculum is unique in that the fringe consists of bunches of bristles with free ends which are not fused to the lamellar blade of the following whorl; fringe has a looser arrangement with fewer bristles than in all other species. The radula resembles that of A. isipingoensis gen. et comb. nov., including the unusual serrated top edge of the rachidian.

Afrocyclus exsertus gen. et comb. nov. is very rare and patchily distributed. Despite searching, it has not been found recently at any of the localities recorded by Connolly (1939) or in several other patches of forest on the Kwazulu-Natal south coast, excepting three very small patches among sugarcane fields, where it was presumably too steep for clearing of original forest. The vegetation on the Kwazulu-Natal south coast has undergone extensive modification since 1939.

Cyathopoma meredithae ( Bruggen, 1983) comb. nov. and Cyathopoma chirindae ( Bruggen, 1986) comb. nov.

Cyathopoma meredithae comb. nov. and Cyathopoma chirindae comb. nov. are removed from genus Chondrocyclus s.l. for three reasons, based on morphology of shell and operculum: i) shells have spiral keels while those of Chondrocyclus s.l. are smooth once the periostracum is removed, ii) opercula are calcareous, while those of Chondrocyclus s.l. are corneous, iii) periostracum is not glossy and lacquerlike as in all Chondrocyclus s.l. species, but is white and matt, suggesting a degree of calcification. C. meredithae ( Bruggen, 1983) comb. nov. and C. chirindae ( Bruggen, 1986) comb. nov. resemble one another in general shape, possession of periostracal hairs at junctions between axial and spiral sculpture, and in the appearance of the operculum, but the latter has more dense axial lamellae and spiral keels ( Fig. 34 ).

Bruggen (1986) erroneously considered major spiral sculpture in the form of keels, ridges or cords to be a diagnostic feature of the Cyclophoridae in Africa. Shells of species of Chondrocyclus s.l. have spiral rows of periostracal projections, but are usually smooth once the periostracum is removed with only traces of axial sculpture. ( Chondrocyclus kevincolei sp. nov. and to a lesser extent C. langebergensis sp. nov. from the Western Cape have spiral engraving.) Cyathopoma meredithae comb. nov. and C. chirindae comb. nov. both have a reticulate surface sculpture with spiral keels and axial lamellae more or less equal in density, with dark brown bristles on the points where the axial and spiral sculpture meet. In both species the periostracum is described as “corneous” ( Bruggen 1983, 1986). However, the periostracum of C. chirindae (NM L4904) ( Fig. 33B ) does not appear to be “corneous”, but is white and matt, suggesting a degree of calcification and this is also apparent to a lesser degree in C. meredithae comb. nov.

The descriptions of their opercula are also identical: duplex with exterior portion in the form of a large, concave, shallow saucer with six–eight spiral whorls ( Bruggen 1983, 1986). Bruggen does not mention whether the opercula are corneous or calcareous. Examination of the operculum of C. chirindae comb. nov. (NM L4904) and the photograph of the operculum of C. meredithae comb. nov. ( Fig. 34A ) shows that both species have a calcareous operculum.

Attempts to assign the abovementioned two species to other genera are complicated by the fact that all other genera of operculate snails in mainland Africa and Madagascar are in need of revision ( Emberton 2009). Until recently, three of the African cyclophorids were placed in Afroditropis Bequaert & Clench, 1936 , a genus characterised by widely spaced spiral keels on the shell, a thin peristome, not reflexed nor flaring, and a thin, corneous, simple operculum. Afroditropis was synonymised with Cyathopoma by de Winter (2002), based on conchological similarity as well as similarities between the opercula of two specimens identified as A. strongi Bequaert & Clench, 1936 , and the opercular structure of Cyathopoma africanum Pilsbry, 1919 , C. straeleni Adam, 1987 and C. camerunense de Winter, 2002 . Whether these genera should be synonymised remains inconclusive since de Winter (2002) did not examine the operculum of the type specimen of A. strongi and he acknowledged that the two specimens on which he based his synonymy may actually represent an as yet undescribed species due to various differences between each of them and A. strongi . The other mainland African genus in Cyclophoridae is Elgonocyclus Verdcourt, 1982 with two species, E. koptawaliensis (Germain, 1934) and an undescribed species from Ongoye forest, Zululand, both minute species with marked axial costulation and simple, corneous opercula.

Recently described African cyclophorids have been placed in Cyathopoma (e.g., C. camerunense de Winter, 2002 ; C. tres Bruggen, 2008 and C. pembense Rowson, 2010 in Rowson et al. 2010b ) and following this trend, Cyathopoma meredithae comb. nov. and C. chirindae comb. nov. were tentatively placed in Cyathopoma ( Cole et al. 2019) . The diagnosis in Blanford (1864) of Cyathopoma relies chiefly on features of the operculum which is usually truncate-conoid, with the concave exterior portion formed by a calcareous, spiral lamella which usually curves inwards towards the centre and is sometimes beautifully sculpted and elevated. The only cyclophorid on mainland Africa with an operculum conforming to this pattern is Cyathopoma tres Bruggen, 2008 , from Malawi, whereas in all the other mainland African species, including Cyathopoma meredithae comb. nov. and C. chirindae comb. nov., the operculum is concave since the erect spiral lamella is higher towards the periphery ( Figs 34 , 35A, C ). There is considerable variation in the opercula of the 60 Malagasy species currently assigned to Cyathopoma s.l. so a future revision may lead to amendment of Blanford’s diagnosis ( Emberton 2003). At the time of the descriptions of Cyathopoma meredithae comb. nov. and C. chirindae comb. nov. the opercula of African Cyathopoma (except C. africanum Pilsbry, 1919 ) were not known because many of the current species had not yet been described (e.g., Cyathopoma straeleni Adam, 1987 , C. camerunense de Winter, 2002 , C. pembense Rowson, 2010 ) or the operculum was not known ( C. azaniense Verdcourt, 1978 ). The opercula of both Chondrocyclus s.l. and Cyathopoma are duplex, with an erect spiral lamella forming the whorls of the exterior portion, but that of Chondrocyclus s.l. is uncalcified ( Kobelt 1902) while that of Cyathopoma is calcareous ( Blanford 1864).

The reticulate surface sculpture of Cyathopoma meredithae comb. nov. and C. chirindae comb. nov. is unlike that of all other mainland African Cyathopoma which have prominent spiral keels and numerous closely set axial riblets. As far as is known, no other mainland African cyclophorids (except Chondrocyclus s.l.) have periostracal bristles. In some species the axial striae grow out into long processes of the periostracum, adhering in groups to the keels, e.g., Cyathopoma africanum Pilsbry, 1919 and C. pembense Rowson, 2010 . It is not known whether such an elaborate periostracum occurs in the other African species because it is easily worn off. The type species of Cyathopoma , C. filocinctum Benson, 1851 , as well as a few Malagasy species ( Emberton 2003), also have reticulate surface sculpture, and a few Malagasy species have periostracal hairs ( Emberton 2003).

The reticulate appearance of Cyathopoma meredithae comb. nov. and C chirindae comb. nov. resembles several species of Malagasy Cyclotus ( Emberton 2004) ( Fig. 36 A–B). In some Malagasy Cyclotus the axial lamellate costae elevate into triangular periostracal projections along the sutural edge and within the umbilicus ( Emberton 2004). In C. chirindae comb. nov. the sharp edged lamellae are raised into small triangular projections at the junctions with the spiral keels and these are particularly dense within the umbilicus ( Fig. 34B ). The operculum of the specimen of Cyclotus examined is flat and bilayered ( Fig. 36 C–D), and resembles that of the type species of Cyclotus , C. variegatus Swainson, 1840 ( Fig. 36E ), the outer surface concave, formed by an inwardly curving, spiral calcareous sheet that increases in elevation towards the periphery and without projections or appendages. Bruggen (1983) draws attention to the similarity between the opercula of C. meredithae comb. nov. and Cyclotus mamillaris Odhner, 1919 (which at the time of Bruggen’s description was classified as Chondrocyclus mamillaris ( Fischer-Piette et al. 1993)) .

Cyathopoma meredithae comb. nov. and C chirindae comb. nov. both have a thin peristome, practically free, but with a limited area touching the body whorl ( Fig. 34 ), but it is not certain whether the specimens examined were adult. In adult Chondrocyclus s.l. the peristome is detached from the last whorl and droops downwards, but in subadults it is attached in a limited area. The peristome of C. filocinctum Benson, 1851 is moderately thick with a broad basal flare, and in several mainland African and Malagasy Cyathopoma it is expanded and may also be thickened.

The radulae and penes of mainland African and Malagasy Cyathopoma and Cyclotus have not been documented prior to this study and no bodies of Cyathopoma meredithae comb. nov. or C. chirindae comb. nov. were available for examination. These features have proved useful in diagnosis and taxonomy of species of Chondrocyclus s.l., so their examination in C. meredithae comb. nov. and C. chirindae comb. nov. may provide useful insights as to their affinities, even though they would probably not assist with generic placement at present. The penis of Cyathopoma pembense is extremely long and narrow relative to that of Chondrocyclus s.l. and does not appear to have an intromittent organ, but tapers to a very fine point ( Fig. 35D ). The penis of Cyclotus sp. from Madagascar resembles that of C. pembense , but has a relatively broader shaft which also narrows to a fine point and no intromittent organ ( Fig. 36 G– H). What appears to be a groove possibly corresponding to a seminal groove, runs down the ventral surface. In both these species the penis lies doubled back on itself.

The radulae of Cyathopoma pembense and Cyclotus sp. differ ( Figs 35B and 36F ). Cyathopoma pembense has a serrated upper edge to the rachidian tooth, also found in Afrocyclus gen. nov., but the first and second lateral teeth have four large cusps (often with extras), unlike the radula of any Afrocyclus gen. nov. or species of Chondrocyclus s.s. The radula of Cyclotus sp. resembles the radulae of several species of Chondrocyclus s.s., with three large cusps on the second lateral tooth. As noted in the Comparative morphological observations section, radulae of various Cyclophoridae look superficially alike, so similarities in the radula do not necessarily imply close relationship.

Figures

Fig. 29. Distribution map of Afrocyclus gen. nov. T indicates type localities. Provinces and major cities are labelled.

Fig. 33. Afrocyclus exsertus (Melvill & Ponsonby, 1903) gen. et comb. nov. A. Holotype (NHMUK 1904.4.29.28). B. Aperture view (ELM D16953). C. Protoconch (ELM D16951). D. Detail of axial lamellae of periostracum (ELM D16951). E. Dorsal view (ELM D16951). F. Ventral view (ELM W3654). G. Portion of radula (ELM W3654). H. Operculum (ELM W3654). I. Penis, dorsal view (ELM W3654). J. Operculum, lateral view (ELM W3655). K. Penis, lateral view (ELM W3654). Scale bars: A = 3 mm; B, E = 1 mm; C, H–K = 500 µm; D = 200 µm; F = 2 mm; G = 50 µm.

Fig. 34. A. Cyathopoma meredithae (Bruggen, 1983) comb. nov., paratype and close-up of operculum (NHMUK 198338). B. Cyathopoma chirindae (Bruggen, 1986) comb. nov. (NMSA L4904). Scale bars: A–B = 1 mm.

Fig. 35. Cyathopoma pembense Rowson, 2010. A–D. ELM D18464. A, C. Operculum. B. Portion of radula. D. Penis, lateral view. Scale bars: A, C–D = 500 µm; B = 20 µm.

Fig. 36. Cyclotus sp. A. Aperture view (NMSA L7108). B. Dorsal view (NMSA L7108). C–D. Operculum (NMSA L7108). E. Cyclotus variegatus Swainson, 1840 operculum (NHMUK1893.6.7.43-5). F. Portion of radula (NMSA L7108). G. Penis, dorsal view (NMSA L7108). H. Penis lateral view (NMSA L7108). Scale bars: A–B = 2 mm; C, E = 1 mm; D, G–H = 500 µm; F = 50 µm.