Prestonella nuptialis ( Melvill & Ponsonby, 1894 )

Herbert, D. G., 2007, Revision of the genus Prestonella (Mollusca: Gastropoda: Orthalicoidea: Bulimulidae s. l.), a distinctive component of the African land snail fauna, African Invertebrates 48 (2), pp. 1-19 : 11-13

Prestonella nuptialis ( Melvill & Ponsonby, 1894)

Figs 8 , 12, 13 , 16–18 , 20–24 , 26–28

Buliminus nuptialis: Melvill & Ponsonby 1894: 92 , pl. 1, fig. 5. Type loc.: ‘ Craigie Burn, Somerset East’ ,

South Africa, leg. Mrs Mary Layard Barber [née Bowker].

Buliminus nuptialis: Sturany 1898: 602 .

Buliminus (Pachnodes) nuptialis: Kobelt 1902: 762 , pl. 111, fig. 22.

Ena nuptialis: Connolly 1912: 172 .

Prestonella nuptialis: Connolly 1939: 293 .

Etymology: The origin of this somewhat unusual species name is explained by a note with the paratype at the RMCA, which states ‘found by goddaughter and sent to me on the eve of her wedding day’; the initials are unclear, but could well be E.L.L. of Edgar L. Layard, who was indeed Mary Bowker’s godfather.

Description ( Figs 8 , 12, 13 ): Shell succineiform to bulimiform, thin; suture weakly to moderately indented. Aperture ovate to roundly D-shaped; upper part of columella lip reflected over umbilical region, but umbilicus remaining relatively widely patent; apertural rim obliquely tangential, and peristome thus in one plane; aperture without teeth, denticles or varices. Sculpture almost devoid of spiral elements (except on protoconch, see below), comprising only relatively strong, somewhat irregular rounded growth-ridges, strongest below suture and somewhat sinuous in this region.

Colour: Shell translucent when fresh, overlain by yellow-ochre to ochre-brown periostracum with irregular darker and lighter bands corresponding with growth-ridges; apex usually only slightly darker; periostracum and underlying shell often heavily eroded, particularly near apex; frequently with adherent particles of debris. Head-foot dark brown.

Dimensions: Length up to 15.5 mm, width up to 10.0 mm; adult L/W 1.37–1.69; body whorl length = 81.4–90.4% of shell length; aperture length = 48.2–62.9% of shell length (N=17).

Protoconch ( Fig. 8 ): Diameter 1.5–1.75 mm, comprising 1.75–2.0 whorls; basic shape similar to that of P. bowkeri , but lacking axial riblets; fine surface detail eroded in most specimens, but traces of microscopic spiral striae present in some; junction between protoconch and teleoconch usually not well defined.

Holotype: SOUTH AFRICA: Eastern Cape: BMNH 1905.1 .26.29, ‘ Craigie Burn’, Somerset East, J.H. Ponsonby Esq. [originally collected by Mrs Mary Layard Barber (née Bowker), and sent by E. L. Layard]; length 11.5 mm ( Fig. 12 ).

Paratype: ‘ Craigie Burn’, Somerset East ( RMCA 26584 ) .

Type locality: The locality cited in the original description, ‘Craigie Burn’, is a farm on the eastern slopes of the Bosberg, south-east of the hill ‘Graskop’ and immediately north of ‘Avon Heights’ farm, co-ordinates 32°41.1'S: 25°40.7'E, altitude approx. 1000 m a.s.l.

Additional material examined: SOUTH AFRICA: Eastern Cape: Cradock area, Elandsberg Mountain (32°07.488'S: 25°42.348'E), approx. 1450 m a.s.l., just below summit, on southern slope, D. Herbert, M. Bursey & G. Redman, 23.i.2002 ( NMSA V9781 ) ; Cradock area, inselberg south of Tarkastad road, near ‘ Plankfontein’ farm (32°07.822'S: 25°47.795'E), 1530 m a.s.l., just below summit on south-facing slope, D. Herbert, M. Bursey & G. Redman, 24.i.2002 ( NMSA V9778 ) ; Cradock area, ‘found in narrow fissures in the rocks on the mountain tops’ (NMSA 1592); Cradock area, Elandsberg Mountain (W901and NMW) ; Cradock ( NMSA B117 , V5275 ) ; Cradock, J. Farquhar ( NMSA W437 ) ; Cradock , ( RMCA 26585 and RBINS) ; Adelaide area, Fenella Falls (32.367°S: 26.367°E), in crevices in rocks behind high waterfall, M. Bursey, v.2007 ( NMSA W5507 ) .

Distribution ( Fig. 16 ): Endemic to South Africa, and recorded only from Eastern Cape province, in the environs of Somerset East and Cradock, and the Winterberge mountain range, at altitudes of 1000–1600 m a.s.l. In the Somerset East area it is only known from the type locality and has not been collected in this area since its description.

Habitat ( Figs 17, 18 ): Living specimens have recently been collected at two localities. Firstly near the summit of two ‘inselbergs’ in the Cradock area, and secondly at the Fenella Falls in the Winterberge.At the Cradock site, the specimens were found wedged in crevices and under overhangs in the near vertical face of a narrow band of reddish mudstone just below the summit of the mountains. The aspect was largely south-facing and thus for the most part shaded. The rock was mostly bare of superficial encrustations. A note stating ‘found in narrow fissures in the rocks on the mountain tops around Cradock’ associated with specimen lot NMSA 1592 indicates that W. Farquhar’s material cited by Connolly (1939) was collected in a similar habitat. In contrast, the Fenella Falls site closely resembled sites at which P. bowkeri has been found—a shaded, gorgelike habitat with a high waterfall, the snails being found in crevices in bare rock walls in the immediate environs of the waterfall. Nothing is known of the precise habitat in which the type specimens were collected at ‘Craigie Burn’.

As with the habitat of P. bowkeri , orographic phenomena associated with these sites will mean that they provide moister habitats than those of the surrounding landscape matrix. In overcast weather, the tops of Karoo inselberg mountains frequently project into the cloud layer (as they did when the Cradock material was collected, Fig. 17 ) and thus will be subject to moist conditions, while the intervening, lower-lying land remains dry and typical of the Nama Karoo biome ( Low & Rebelo 1996).Although not measured, the temperature near the Elandsberg summit was significantly cooler, and made more so by wind.At Fenella Falls, mist associated with the Winterberge mountains combined with wind-blown spray from the waterfall and the shaded aspect of the habitat are likely result in relatively mesic conditions.

Notes: Differs from P. bowkeri in being smaller and generally broader with more convex whorls (but adult L/W ratios overlap, Table 2), and in lacking both fine granular sculpture on the adapical surface of the spire whorls and axial riblets on the protoconch. The living animal is of a much darker colour than that of P. bowkeri . P. quadingensis (below) is identical, except that it possesses fine spiral sculpture on later whorls, has axial riblets on the protoconch and is perhaps slightly more obese.

Figures

Figs 7, 8. Prestonella protoconchs: (7) P. bowkeri, Nuweveldberg, Beaufort West (SAM, A8171); (8) P. nuptialis, protoconch. Scale bars = 0.5 mm.

Figs 12–15. Prestonella nuptialis (Melvill & Ponsonby, 1894) and P. quadingensis Connolly, 1932: (12) P. nuptialis holotype, length 11.5 mm (BMNH 1905.1.26.29); (13) undamaged specimen, Cradock, length 13.3 mm (NMSA 1592); (14) P. quadingensis holotype, length 12.2 mm (NMSA J8135/T2835); (15) paratype, length 11.4 mm (BMNH 1937.12.30.7079-80).

Fig. 16. Distribution of Prestonella nuptialis (9) and P. quadingensis ().

Figs 17, 18. Habitat of Prestonella nuptialis, Elandsberg, Cradock: (17) Elandsberg with its summit in cloud, on a day when no rainfall was recorded in the surrounding landscape; (18) vertical rock faces near summit, with crevices and overhangs in which the species lives.

Figs 19, 20. Prestonella bowkeri and Prestonella nuptialis, living specimens: (19) P. bowkeri, shell length 18.0 mm, Glen Avon Falls (NMSA V9816); (20) P. nuptialis, shell length 13.0 mm, Fenella Falls (NMSA W5507).

Figs 21–25. Prestonella radulae:(21–24) P. nuptialis (NMSA V9778): (21) central field and inner marginals (rachidian and laterals numbered), scale bar = 50 µm; (22) rachidian (R) and inner laterals, scale bar = 25 µm; (23) outer marginals, scale bar = 25 µm; (24) latero-marginal transition, scale bar = 25 µm; (25) P. bowkeri (NMSA V9816) latero-marginal transition, scale bar = 25 µm.

Fig. 26. Prestonella nuptialis jaw, extended through mouth after drowning (NMSA W5507).

Figs 27, 28. Prestonella nuptialis (NMSA V9778): (27) pulmonary anatomy (abbreviations: an – anus, aur – auricle, int – intestine, kid – kidney, pc – pericardium, pn – pneumostome, pu – primary ureter, pv – pulmonary vein, rec – rectum, su – secondary ureter, urp – ureteric pore, ven – ventricle); (28) genital anatomy (abbreviations: alb – albumen gland, bc – bursa copulatrix, eph – epiphallus, flg – flagellum, ga – genital atrium, hd – hermaphrodite duct, od – oviduct, ot – ovotestis, pen – penis, pr – prostate gland, prm – penis retractor muscle, vd – vas deferens).