Afrorhytida burseyae, Herbert & Moussalli, 2010

Herbert, D. G. & Moussalli, A., 2010, Revision of the larger cannibal snails (Natalina s. l.) of southern Africa - Natalina s. s., Afrorhytida and Capitina (Mollusca: Gastropoda: Rhytididae), African Invertebrates 51 (1), pp. 1-1 : 98-103

Afrorhytida burseyae sp. n.

Figs 10B , 54D , 55G , 66–69

Etymology: Named for Mary Bursey (now Cole), malacologist at the East London Museum who has collected much valuable land snail material and helped enormously with field logistics.

Identification: Shell very similar to that of elevated specimens of A. knysnaensis , but with a somewhat narrower umbilicus. Differs consistently from that species in having more lateral teeth and fewer marginal teeth in the radula ( Table 2), and comprises a distinct genetic lineage within Afrorhytida . Evidently restricted to the region encompassing the catchments of Kei and Mbashe rivers, whereas A. knysnaensis occurs further to the west, in the catchments of the Sundays and Great Fish rivers.

Description ( Fig. 66 ): Shell subglobose, somewhat turbiniform; comprising up to 4.5 whorls, last adult whorl descending prior to aperture, but sometimes only weakly so; base glossy, apical surface less so, but still retaining some lustre when fresh. Protoconch 4.4–5.0 mm in diameter; apical portion more or less smooth, axial riblets developing during first whorl, initially weak, but strengthening toward end of whorl; protoconch/ teleoconch junction usually poorly defined. Apical surface of teleoconch sculptured by close-set axial riblets, these becoming weaker and less well defined toward end of last adult whorl and on base; traces of weak, close-set, spiral liration between axial riblets, particularly on base; aperture subcircular to roundly-ovate; outer lip slightly thickened basally though scarcely so elsewhere (but most specimens slightly subadult and lip rather thin throughout); upper part of outer lip not flattened; umbilicus narrow, its margin rather steeply curving, partially obscured by reflected upper portion of columella lip in adults.

Fresh specimens more or less uniformly yellow-ochre to olive-green; little difference between apical and basal surfaces; occasional very slightly darker radial bands may be present.

Dimensions: Holotype, diameter 21.1 mm, height 17.5 mm; largest specimen (NMSA V6634, ‘Pondoland’), diameter 26.4 mm; H:D of adults 0.74–0.87 (N=16).

Living animal ( Fig. 55G ): Head-foot pale apricot-orange to pale grey-brown; neck region somewhat darker brown, sometimes with a paler, dorsolateral, longitudinal stripe on each side extending backwards from optic tentacle; tentacles darker grey; sides of foot generally pale, often with a narrow orange band at pedal margin; mantle edge greyish white to apricot-orange; lung wall with limited black pigmentation.

Radula ( Fig. 67 ): Formula 1+(12–14)+(7–9) (N=4); length up to 15.4 mm, with 60–70 V-shaped rows of teeth, 4.3–4.6 rows/mm in adult. Rachidian cusp somewhat longer than its base-plate. Inner lateral teeth (1–10) differing little in size, long and slender, more or less parallel-sided, apically acuminate with the tip sometimes slightly curved outward; outermost 3 or 4 lateral teeth increasing rapidly in size and developing stout quadrate base-plate, with relatively slender, gently curved, sharply pointed cusp; penultimate lateral is the largest. Innermost marginal tooth relatively large (approx. 0.66 length of outer lateral), second marginal retaining distinct cusp but subsequent marginals vestigial.

Distal genitalia: Epiphallus approx. 75 % length of penis; thick-walled for most of its length and frequently strongly curved; lumen wall with low, indistinct ridges between which are numerous, close-set, transverse pockets, representing openings of diverticulae in epiphallus wall ( Fig. 54D ); these concentrated in middle two-thirds corresponding with spinose mid-piece of spermatophore; sparse toward vas deferens and junction with penis.

Spermatophore ( Fig. 68 ): Well preserved allospermatophores have been found in the female tract of two specimens collected in early March, one per specimen. Spermatophore white to pale pink, U-shaped and of firm texture, evidently variable in size (about 6.5 mm and 10.5 mm in total length); comprising three distinct regions, a bluntly acuminate head, a broader, U-shaped mid-piece and a short, recurved tail. Inner surface of bend with a deep, longitudinal depression or groove, but otherwise spermatophore lacking strong longitudinal grooves/ridges; outer surface of mid-piece bearing numerous, small, close-set, forwardly directed, spine-like projections pressed flat against its surface; spines compound (finely branched apically); tail and head piece with few spines. No obvious vent present in the tail region, but spermatophore contents visible in inner groove of mid-piece in one specimen.

Spermatophores situated in upper part of vagina, in one specimen the head extended into base of free oviduct, in the other it extended into base of bursa copulatrix duct.Anterior half of mid-piece level with origin of bursa copulatrix duct and end of free oviduct, tail extending backward into lower, longitudinally ridged portion of vagina.

Surprisingly the spines on the mid-piece are directed toward the head region, an orientation which might impede rather than facilitate the passage of the spermatophore within the vagina, suggesting that it is deposited in this position by the penis of the partner during copulation. Even so, this orientation would seem to hinder its release from the epiphallus into the penis. The spines, however, appear less rigid than in other species suggesting a degree of flexibility. They may serve an anchoring function, holding the spermatophore in place once deposited.

Holotype ( Figs 66A–C ): SOUTH AFRICA: E. Cape: Wedgeley farm, Kei R. valley, NNE of Stutterheim, (32.28986°S: 27.54674°E), 845 m, grassy bushveld, crawling at night on grass and stones beside farmhouse after rain, D. Herbert & L. Davis, 4/iii/2007 ( NMSA W5228 /T2257).

Paratypes: SOUTH AFRICA: E. Cape: same data as holotype ( ELM D15855 , 1 specimen; BMNH 20100126 , 1 specimen; NMSA W5229 /T2258, 3 specimens; NMSA W5230 /T2259, 1 specimen; NMSA W5231 /T2260, 1 specimen) ; Engcobo (31.66°S: 28.00°E), ca 975 m ( SAMC A11289 , 1 specimen) ; Cathcart (32.29241°S: 27.13567°E), 1210 m, montane grassland/bushveld, small juvenile on grass blade, A. Moussalli, D. Stuart-Fox & M. Bursey, 30/xi/2005 ( NMSA W4844 /T2261, 1 specimen, juvenile) ; Sterkstroom, Koos Ras Nat. Res. (31.54935°S: 26.57283°E), 1440 m, rocky outcrop with trees and shrubs, buried under grass clump, Herbert, Davis, Cole & Fearon, 09–005, 29/iii/2009 ( NMSA W6712 /T2489, 2 specimens, subadult) ; Mbashe River valley nr N2 bridge (31.92461°S: 28.45113°E), 465 m, riverine thicket, in leaf-litter and under fallen aloes, A. Moussalli & D. Stuart-Fox, 23/xi/2005 ( NMSA W5372 /T2349, 3 specimens) ; Kei Pass (32.49364°S: 27.99175°E), 270 m, valley thicket, under rocks, A. Moussalli & D. Stuart-Fox, 23/xi/2005 ( NMSA W5484 / T2347, 1 specimen) ; Gonubie R., Slippery Drift (32.80055°S: 27.85583°E), ca 200 m, Jansen, 28/xii/2002 ( ELM D13766 , 1 specimen) ; East London area, 20 km inland, nr Nahoon Dam, Elizweni resort (32.915297°S: 27.818867°E), 140 m, thicket on north facing slope above Nahoon R., in leaf-litter, M. Bursey, 18/i/2007 ( NMSA W5252 /T2346, 2 specimens) ; ditto, Elizweni resort, on west bank of Nahoon R., M. Bursey, 18/iv/ 2006 ( ELM D14971 , 5 specimens) ; Berlin area, Mncotsho, Buffalo R. valley (32.917°S: 27.583°E), ca 360 m, grassland with scattered bushes near beacon, M. Cole & C. Vernon, 06/xi/2007 ( NMSA W6004 /T2348, 3 specimens) .

Other material examined: SOUTH AFRICA: E. Cape: Bailey , ca 1300 m, Miss Hickey ( NMSA B0097 ) ; Ugie , ca 1300 m, Miss L. Britten, i/1923 ( NMSA E7906 ) ; ‘ Pondoland’, Mrs A. Filmer ( NMSA V6842 , V6634 ) .

Distribution ( Fig. 69 ): Endemic to E. Cape; recorded primarily from inland localities in the Great Kei River catchment and eastwards to the Mbashe and Mzimvubu catchments, but recorded also from smaller coastal drainage systems in the East London area (Buffalo, Nahoon and Gonubie rivers); occurs at altitudes of 140–1440 m.

Habitat: Evidently favours somewhat open habitats rather than forest; recorded from a range of vegetation types including grassy bushveld, montane shrubland and various types of thicket; hiding under fallen aloes and in grass clumps between rocks.

Notes: This species was initially thought to represent Natalina eumacta ( Melvill & Ponsonby, 1892) . However, examination of the holotype of that species BMNH (1905.1.26.2, Figs 24A–C ) shows it to be considerably larger (diameter 30.3 mm) than any specimens of the present species. In addition it is not as globose, has a larger protoconch and lacks any thickening of the aperture lip.We consider that N. eumacta represents the eastern coastal subspecies of Natalina cafra (see above).

The shell of Afrorhytida burseyae closely resembles that of elevated specimens of A. knysnaensis such as occur in the Greater Fish River Conservancy, and indeed it cannot be reliably distinguished from such specimens on shell features alone.Although few specimens have been observed alive, the head-foot colour of A. burseyae also resembles that of some specimens of the variably coloured A. knysnaensis and, given this variability in the latter species, body colour also seems unlikely to prove useful for species discrimination. However, the radula of A. burseyae differs markedly and consistently from that of A. knysnaensis in having many fewer marginal teeth and in the penultimate rather than the outmost lateral being largest. In these features it resembles A. trimeni from which it differs conchologically in having a considerably more globose, yellowish green rather than brown shell, with weaker axial sculpture and a much narrower umbilicus. Molecular data confirms that A. burseyae constitutes a distinct lineage within the Afrorhytida radiation, though its relationships to the other species are not resolved ( Moussalli et al. 2009). Its radula morphology suggests that it is perhaps most closely related to A. trimeni , whereas its epiphallus morphology is closer to that of A. kraussi ( Fig. 54 ).

Conservation: Although few specimens of Afrorhytida burseyae are available, it occurs in a very poorly sampled area and it may not be scarce where conditions are favourable. Its known extent of occurrence is considerable (approx. 15,000 km 2) and given that it favours open habitats, its area of occupancy is not likely to be particularly limited or fragmented. Thus despite being a newly discovered taxon, it seems unlikely that A. burseyae is threatened at present. In the long term, however, the continued transformation of natural habitats, associated with agricultural expansion, represents a potential threat, particularly so since the distribution of A. burseyae currently includes very few, if any, formally conserved areas.

Figures

Fig. 10. Spermatophores of Capitina, Afrorhytida and Natalina (all NMSA):(A) C. calcicola sp. n. (paratype, W5670/T2265), length 8.2 mm; (B) A. burseyae sp. n. (paratype, W5231/T2260), length 10.5 mm; (C) A. kraussi kraussi (W5803), length 20 mm; (D) N. cafra natalensis subsp. n. (paratype, E7682/T2375), length 16.3 mm; (E) N. quekettiana lucaris subsp. n. (paratype, W3305/T2559), length 26.5 mm; (F) N. wesseliana (V7668), length 32 mm. The head of the spermatophore is uppermost in all cases and the lengths given are for the spermatophore as if straightened out.

Fig. 54. Penis and epiphallus of Afrorhytida species, cut open longitudinally to show internal structure (all NMSA): (A) A. knysnaensis, penis (W4248, Cradock); (B) A. knysnaensis, epiphallus (W4643, Somerset East); (C) A. trimeni, epiphallus (W4206, Kap R.); (D) A. burseyae sp. n., epiphallus (paratype, W5231/T2260); (E) A. kraussi kraussi, epiphallus (V6578, Wilderness). Abbreviations: d – diverticulae in epiphallus wall, dp – digit-like pilaster at end of ridge, ep – epiphallus, er – internal epiphallic ridge, ga – genital atrium, lg – longitudinal groove between well-developed folds on inner side of epiphallus, p – penis, pl – penis lumen with papillate lining, pr – penial retractor muscle, v – vagina, vd – vas deferens.

Fig. 55. Afrorhytida species, living animals (all NMSA): (A) A. knysnaensis, Fort Beaufort (W5211), shell diameter 19.0 mm; (B) A. knysnaensis, Cradock (W4248), shell diameter 22.0 mm; (C) A. knysnaensis, Kompasberg, Nieu Bethesda (W6097), shell diameter 20.4 mm; (D) A. kraussi kraussi, Featherbed Nat. Res., Knysna (W4671), shell diameter 16.8 mm; (E) A. k. kraussi, Grootvadersbosch (W5803), shell diameter 23.8 mm; (F) A. kraussi oraria subsp. n., De Hoop Nat. Res. (paratype, W3292/T2363), shell diameter 13.4 mm; (G) A. burseyae sp. n., Wedgeley farm, Kei River Valley (paratype, W5229/T2258), shell diameter 19.3 mm; (H) A. trimeni, Kap River (W4206), shell diameter 24.5 mm.

Fig.66. Afrorhytida burseyae sp. n.: (A–C) holotype (NMSA W5228/T2257), diameter 21.1mm; (D) Engcobo, paratype (SAMC 11289), diameter 23.8 mm; (E) Kei Pass, paratype (NMSA W5484/T2347), diameter 21.8 mm.

Fig. 67. Afrorhytida burseyae sp. n., radula (holotype, NMSA W5228/T2257): (A) half width of radula, scale bar = 250 µm; (B) rachidian and inner lateral teeth, scale bar = 100 µm; (C) lateromarginal transition zone, scale bar = 100 µm (l – outer lateral; m – inner marginal); (D) marginal teeth [7], scale bar = 50 µm.

Fig. 68. Afrorhytida burseyae sp. n., spermatophore (paratype, NMSA W5231/T2260): (A) in situ in dissected upper portion of vagina and lower free oviduct, (B) extracted spermatophore, total length 10.5 mm. Abbreviations: bd – bursa copulatrix duct, fo – free oviduct, m – mid-piece of spermatophore, s – spermatophore, sh – spermatophore head, sp – spines on outer surface of mid-piece, st – spermatophore tail, v – vagina.

Fig. 69. Distribution of Afrorhytida burseyae sp. n. Triangles with a white centre indicate localities for specimens used in DNA analyses (Moussalli et al. 2009); contours at 1000 m and 1500 m.

Fig. 24. Natalina cafra eumacta (Melvill & Ponsonby, 1892): (A–C) lectotype (juvenile) of Helix (Aerope) eumacta Melvill & Ponsonby, 1892 (BMNH 1905.1.26.2), diameter 30.3 mm; (D) juvenile, Holme Park farm, Komga District (NMSA W5990), diameter 36.6 mm; (E–G) adult, Dwesa Nat. Res. (NMSA V7868), diameter 51.8 mm.