Afrorhytida kraussi oraria, 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 : 96-98

Afrorhytida kraussi oraria subsp. n.

Figs 55F , 63 , 64E , F, 65A–C

Etymology: From orarius (Latin) , of the coast; referring to its association with coastal fynbos and dune strandveld habitats.

Identification ( Fig. 65 ): For general description see Afrorhytida k. kraussi above. Shell shape and sculpture resembling A. k. kraussi , but with distinctive coloration (see below); protoconch smaller (diameter 2.5–3.0 mm) and shell thicker. Does not appear to attain as large a size as the nominotypical subspecies (diameter of largest specimens 23.1 and 28.4 respectively), but adult size evidently varies considerably in the latter.

Periostracum very thin, pale buff, not evident in most specimens; underlying shell mostly whitish with apical region frequently darker, pinkish purple to maroon; last adult whorl often with occasional, irregular, purplish or maroon-brown axial bands, particularly behind outer lip of adult. Shell also sparsely pock-marked with small, dark flecks, these often associated with small growth imperfections; interior of aperture buffish in fresh specimens, the darker subterminal band, if present, visible through shell.

Dimensions: Holotype, diameter 22.3 mm, height 13.3 mm; largest specimen ( NMSA W3297 ), diameter 23.1 mm, height 13.3 mm; H:D of adults 0.56–0.64 (N=12).

Living animal (data available for only one specimen) ( Fig. 55F ): Head-foot coloration similar to that of typical A. k. kraussi , but somewhat darker maroon-brown, very dark dorsally; pedal margin tinged with orange; mantle edge similarly maroon-brown; lung wall with some irregular dark pigmentation, mostly tracking underlying blood vessels.

Radula ( Figs 64E–F ): As in A. k. kraussi .

Distal genitalia: All live-taken material immature.

Holotype ( Figs 65A–C ): SOUTH AFRICA: W. Cape: De Hoop Nat. Res. (34.450°S: 20.383°E), 60 m, W. Sirgel, don. i/1999 ( NMSA V6780 /T2361).

Paratypes: SOUTH AFRICA: W. Cape: De Hoop Nat. Res. (34.47512°S: 20.51969°E), coastal dune scrub, in leaf-litter, A. Moussalli & D. Stuart-Fox, 24/ii/2005 ( NMSA W3292 /T2363, 1 juvenile specimen; W3297/ T2362, 8 adult specimens, 2 juveniles; ELM D15857 , 1 specimen); De Hoop Nat. Res., around Koppie Alleen (34.4667°S: 20.5167°E), ground-dwelling in strandveld, A. Wood, 22/viii/1994 ( NMSA W5776 / T2364, 2 specimens) .

Distribution ( Fig. 63 ): A narrow-range endemic; known only from the De Hoop Nature Reserve, W. Cape, South Africa, at altitudes of <100 m.

Habitat: Recorded only from De Hoop limestone fynbos and Overberg dune strandveld (cf. Mucina & Rutherford 2006); in sandy soil beneath forbs, shrubs and bushes.

Notes: The considerable degree to which Afrorhytida k. oraria differs in shell characters from the nominotypical subspecies would traditionally result in it being considered a distinct species. However, in the analysis of molecular data undertaken by Moussalli et al. (2009), this De Hoop material clustered within the broader assemblage of material considered to represent the A. kraussi complex. Its radula too is indistinguishable from that of members of this complex.Although this assemblage exhibits considerable genetic diversity and may ultimately be shown to be an aggregate of sibling taxa, with the exception of specimens from De Hoop, we have been unable to identify any consistent spatially or genetically correlated patterns in the morphological variation evident. However, since this De Hoop material is clearly conchologically distinct, we consider it merits nomenclatural recognition as a diagnosable entity, ranked for the present as a subspecies. We are aware, however, that some of the conchological characters of this coastal lineage may relate to environmental conditions, particularly edaphic characters (calcium-rich soils) and this is a topic requiring further study.

Conservation: Afrorhytida k. oraria is evidently a taxon of restricted range, but it occurs in a surprisingly poorly sampled area and additional survey work is needed in order to obtain a clearer picture of its distribution.Although currently known only from De Hoop Nature Reserve, the coastal limestone habitat, which it evidently favours, extends considerably beyond the confines of this reserve in the broader Bredasdorp–Stilbaai area. The taxon may thus have a somewhat less restricted distribution than the available data indicate. A meaningful assessment of its threat status must await further information, but this notwithstanding, potential threats are evident, particularly habitat transformation due to the invasion of exotic Acacia species.

Figures

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. 63. Distribution of Afrorhytida kraussi (Pfeiffer, 1846): A. k. kraussi (triangles), A. k. oraria subsp. n. (squares). Symbols with a white centre indicate localities for specimens used in DNA analyses (Moussalli et al. 2009); contours at 1000 m and 1500 m.

Fig. 64. Afrorhytida kraussi (Pfeiffer, 1846), radula (all NMSA): (A–D) A. k. kraussi: (A–C) Diepwalle, Knysna (W4845): (A) entire width of radula, scale bar = 0.5 mm; (B) rachidian and inner laterals, scale bar = 250 µm; (C) outer lateral base-plates and marginals, scale bar = 200 µm (l – outer lateral; m – inner marginal); (D) Grootvadersbosch (W3351), half-row, scale bar = 0.5 mm; (E, F) A. k. oraria subsp. n., De Hoop (paratype, W3292/T2363); (E) half-row, scale bar = 100 µm; (F) outer lateral base-plates and marginals, scale bar = 100 µm.

Fig. 65. Afrorhytida kraussi (Pfeiffer, 1846) (all NMSA): (A–C) A. k. oraria subsp. n., holotype (fresh specimen, V6780/T2361), De Hoop Nat. Res., diameter 22.3 mm; (D) A. k. kraussi, protoconch, Wilderness (V6578); (E) A. k. oraria subsp. n., protoconch, De Hoop Nat.Res. (paratype, W3292/ T2363). Scale bars = 2.0 mm; arrows mark protoconch/teleoconch junction.