Gulella calcicola, Cole & Herbert, 2022

Cole, Mary L. & Herbert, David G., 2022, Eight new species of Gulella Pfeiffer, 1856 from the south-east coast of South Africa (Gastropoda: Streptaxidae), European Journal of Taxonomy 813, pp. 1-32 : 18-22

Gulella calcicola sp. nov.

urn:lsid:zoobank.org:act:6A1FFB5F-2C72-45C8-AB35-25939FC90636

Figs 6A–B , 8A–D

Diagnosis

Shell minute, sub-cylindrical; smooth and glossy; aperture markedly constricted by teeth, slightly deflected to left in apertural view, peristome thickened and reflected. Apertural dentition four-fold including a parietal lamella, with outer portion oblique and then curving inward, a large, square labral tooth, its upper margin sinuous and with a small denticle near lip edge and another further into aperture,

a deeply inset basal peg-like tooth, and a very large inset scoop-shaped columella lamella; apertural tube behind columella lip somewhat inflated and collar-like; umbilicus very small and comma-shaped.

Etymology

From ' calx ' (Latin) = 'lime' and '- cola ' (Latin) = 'an inhabitant', with reference to its distribution at the Marble Delta, KwaZulu-Natal, the largest and most important limestone outcrop in the province.

Material examined

Holotype SOUTH AFRICA – KwaZulu-Natal • Port Shepstone area, Marble Delta , immediately upstream of confluence of Mzimkulu and Mzimkulwana Rivers, between Port Shepstone and Oribi Gorge Nature Reserve, on northern bank of Mzimkulu River, dense valley thicket, heavily invaded with Lantana and Chromolaena ; 30.6509°S, 30.3560°E; 5 Dec. 2001; D. Herbert leg.; NMSA P1675/T4519 .

Paratypes SOUTH AFRICA – KwaZulu-Natal • 6 specs.; same collection data as for holtype; NMSA V9686/ T4492 • 2 specs.; same collection data as for holotype; NMW.Z.2021.012.00005 , prev. NMSA V9686 • 1 spec.; same collection data as for holotype; RMNH.MOL.452591 , prev. NMSA V9686 • 1 spec.; same locality as for holotype; 5 Oct. 2001; Herbert and M. Bursey leg. D.; NMSA V9401/T4491 • 1 spec.; same collection data as for preceding; ELMD 18760/T231 , prev. NMSA V9401 • 1 spec.; Marble Delta, North side of Mzimkulu River, Q5, steep indigenous forest ; 30.655371° S, 30.37531° E; 4 May 2011; leg. J. Harvey; NMSA W8103/T4489 • 2 specs.; Marble Delta, north side of Mzimkulu River, Q14, indigenous forest , slightly rocky; 30.6519° S, 30.3724°E; 4 May 2011; J. Harvey leg.; NMSA W8068/ T4517 • 2 specs.; Marble Delta, North side of Mzimkulu River, Q8, steep indigenous forest ; 30.6545° S, 30.3764° E; 4 May 2011; J. Harvey leg.; NMSA W8073/T4493 • 2 specs.; Marble Delta, North side of Mzimkulu River, Q12, rocky indigenous forest ; 30.653754°S, 30.370989° E; 4 May 2011; J. Harvey leg.; NMSA W8067/T4490 • 3 specs.; Marble Delta, North side of Mzimkulu River, Q13, indigenous forest , slightly rocky; 30.6529°S, 30.3717° E; 4 May 2011; J. Harvey leg.; NMSA W8062/T4488 • 2 specs.; same collection data as for preceding; NHMUK 20210075 , prev. NMSA W8062 .

Other material

SOUTH AFRICA – KwaZulu-Natal • 3 specs.; Port Shepstone area, Marble Delta, North side of Mzimkulu River, Q18, thicket; 30.6506° S, 30.3633° E; 4 May 2011; J. Harvey leg.; NMSA W8069 • 3 specs.; Marble Delta, North side of Mzimkulu River, Q8, steep indigenous forest ; 30.6545°S, 30.3764°E; 4 May 2011; J. Harvey leg.; NMSA P1614 , prev. NMSA W8073 .

Description

SHELL ( Fig. 8 ). Shell minute, sub-cylindrical, length 1.9–2.2 mm, width 0.8–1.0 mm, L:W 2.1–2.5 (n = 13). Protoconch approx. 0.7 mm in diameter, comprising approx. 2.5 whorls, smooth; junction between protoconch and teleoconch not distinct. Teleoconch comprising approx. 3.5 whorls; convex; smooth and glossy but with weak axial pleats around umbilicus ( Fig. 8A–B, D ). Aperture markedly constricted by teeth, slightly deflected towards left in apertural view; peristome thickened and reflected ( Fig. 8A, C ). Apertural dentition four-fold ( Fig. 8C ): 1) a parietal lamella, with outer portion oblique and then curving inward so that remainder runs into aperture, lower margin sometimes weakly notched; 2) a large square labral tooth, its upper margin sinuous and with a small denticle near lip edge and another further into aperture; 3) a deeply inset peg-like basal tooth; 4) a very large, even more deeply inset rounded, scoop-shaped columella lamella, largely obscured by labral tooth. Labral tooth corresponds with a deep pit behind outer lip ( Fig. 8B ). Apertural tube behind columella lip somewhat inflated and collar-like; umbilicus very small and comma-shaped ( Fig. 8D ). Shell almost transparent when fresh, orange-red coloration of dried tissue of animal visible internally.

Distribution ( Fig. 6 )

Known only from the Marble Delta, an area of ca 40 km 2 at the junction of the Mzimkulu and Mzimkulwana Rivers, inland of Port Shepstone in southern KwaZulu-Natal. Based on existing records, it occurs only on the portion of the limestone deposit that lies to the north-east of the Mzimkulu River.

Habitat

Patches of valley thicket (Low & Rebelo 1996), also referred to as Eastern Valley Bushveld ( Rutherford et al. 2006) and KwaZulu-Natal Scarp forest ( Mucina et al. 2018b); in leaf-litter and under logs. The indigenous vegetation has been heavily invaded by alien plants, notably Chromolaena odorata (L.) R M.King ( Asteraceae ), and Lantana camara L. ( Verbenaceae ), both from South and Central America.

Remarks

The labral complex of Gulella calcicola sp. nov. resembles that of G. crookesi sp. nov., particularly due to the upper margin with a denticle near the lip edge and another further into the aperture. However, the portion furthest into the aperture is square in G. calcicola while that of G. crookesi sp. nov. is triangular. The other apertural teeth all differ between these two species. Gulella farquhari is also somewhat similar, but possesses axial sculpture (if only subsutural riblets) and its labral tooth is proportionally smaller and does not obscure the columella lamella to such an extent.

Conservation

Gulella calcicola sp. nov. has been found only at the Marble Delta, which stands out as the largest and most important limestone outcrop in the province, with a calcium concentration of ca 4000 mg /l ( Herbert 2002). Like G. salpinx Herbert, 2002 , it appears to be a holoendemic taxon (sensu Richardson 1978; Van Wyk & Smith 2001) that has evolved in response to the environmental conditions prevailing in the Marble Delta, perhaps chiefly those associated with soil chemistry. Much of the Marble Delta is now badly degraded as a result of mining operations and the invasion of alien plants. Mining continues in the area and the habitat of the species must thus be considered threatened. The species meets the criteria for red listing as Critically Endangered. A recommendation made by Herbert (2002) is echoed here, namely that mining operations not be conducted on a section of the northern bank of the Mzimkulu River, in an attempt to preserve the habitat as much as possible (acknowledging that alien plants will already have altered this to some extent). Some local indigenous habitat is formally preserved at Oribi Gorge Nature Reserve, upstream on the Mzimkulwana River, but this does not lie within in the Marble Delta area and its soils, derived from decomposed granite and sandstone, have a much lower calcium content ( Herbert 2002). No specimens of Gulella calcicola sp. nov., G. salpinx or G. donaikeni sp. nov. have been found in the Oribi Gorge reserve despite its malacofauna being relatively well-known.

Figures

Fig. 6. A. Distribution map of Gulella donaikeni sp. nov. (red circles) and G. calcicola sp. nov. (blue triangles) in the Marble Delta region of southern KwaZulu-Natal. B. Google Earth image of distribution of G. donaikeni (red symbols) south of the Mzimkulu River and G. calcicola (blue symbols) north of the Mzimkulu River.

Fig. 8. Gulella calcicola sp. nov., holotype (NMSA P1675/T4519), length 2.05 mm, width 0.90 mm. A. Aperture view. B. Side view. C. View into aperture. D. Oblique view of base showing umbilicus. Scale bar = 0.5 mm.