Nata vernicosa ( Krauss, 1848 )

David G. Herbert & Adnan Mousalli, 2016, Revision of the dwarf cannibal snails (Nata s. l.) of southern Africa — Nata s. s. and Natella (Mollusca: Gastropoda: Rhytididae), with description of three new species, Zootaxa 4094 (1), pp. 1-67 : 33-35

Nata vernicosa ( Krauss, 1848) sensu lato

Figure 24

Helix vernicosa Krauss, 1848: 76 , pl. 4, fig. 23. Pfeiffer, 1849: 93. Reeve, 1851: sp. 198, pl. 43. Morelet, 1889: 19. Herbert & Warén, 1998: 235. Type loc.: ‘ in terra natalensi ’ [Wahlberg].

Helix vernicosa β. minor Pfeiffer, 1853: 95 . Type loc.: ‘ Natal Africae meridionalis ’.

Helix (Pella) vernicosa — Pfeiffer, 1879 in 1878 –1881: 102.

Elaea vernicosa — Tryon, 1885: 130, pl. 28, figs 52–54 [as E. verrucosa [sic] in plate legend].

Elaea vernicosa var. minor — Tryon, 1885: 131.

Helix (Macrocyclis) caenotera Melvill & Ponsonby, 1892b: 238 , pl. 13, fig. 2. Type loc.: 'Tharfield', E. Cape [Dr Schönland].

Helix (Macrocyclis) liparoxantha Melvill & Ponsonby, 1892b: 238 , pl. 13, fig. 3. Type loc.: 'Maritzburg' [H.C. Burnup].

Natalina caenotera —Pilsbry, 1893 in 1892–1893: 135. Melvill & Ponsonby, 1898b: 170. Connolly, 1912: 92.

Natalina liparoxantha —Pilsbry, 1893 in 1892–1893: 135. Melvill & Ponsonby, 1898b: 170. Connolly, 1912: 96.

Natalina vernicosa —Pilsbry, 1893 in 1892–1893: 135. Sturany, 1898: 31. Connolly, 1912: 97.

Natalina chaplini Melvill & Ponsonby, 1894: 91 , pl. 1, fig. 3. Melvill & Ponsonby, 1895: 165, pl. 12, figs 5, 5b. Melvill & Ponsonby, 1898b: 170. Sturany, 1898: 31. Connolly, 1912: 92. Type loc.: 'Karnachs' [?=Kamesh], near Port Elizabeth, E. Cape [J. Crawford].

Rhytida kraussi [non Pfeiffer, 1846]— Moss, 1894: 25, pl. 1, fig. 3.

Rhytida Kraussii [sic] [non Pfeiffer, 1846]— Cooke, 1895: 232, fig. 139.

Macrocyclis coenotera [sic]— Sturany, 1898: 32.

Macrocyclis liparoxantha — Sturany, 1898: 33.

Natalina caffrula [non Melvill & Ponsonby, 1898]— Sturany, 1898: 32. Germain, 1935: 5: Haas, 1936: 18 (in part, Umfolozi).

Rhytida vernicosa — Melvill & Ponsonby, 1898b: 170.

Rhytida (Macrocycloides) vernicosa — Möllendorff & Kobelt, 1903, in 1903 –1905: 57, pl. 10, figs 12–14. Kobelt, 1909: 53.

Rhytida (Macrocycloides) chaplini — Möllendorff & Kobelt, 1903, in 1903 –1905: 58, pl. 10, fig. 15–17. Kobelt, 1909: 53.

Rhytida (Macrocycloides) liparoxantha — Möllendorff & Kobelt, 1903, in 1903 –1905: 58, pl. 10, fig. 18. Kobelt, 1909: 53.

Rhytida (Macrocycloides) coenotera [sic]— Möllendorff & Kobelt, 1903, in 1903 –1905: 59, pl. 10, fig. 19. Kobelt, 1909: 53.

Natalina vernicosa var. minor — Connolly, 1912: 98.

Nata vernicosa — Watson, 1934: 161. Connolly, 1939: 99, pl. 4, figs 4, 5, text fig. 6. Zilch, 1959 –60: 554, fig. 1936. Bruggen, 1966: 376, fig. 54. Bruggen, 1967: 29. Bruggen, 1969: 37. Bruggen, 1970: 468. Bruggen, 1978: fig. 3i. Bruggen, 1985: 286. Bruggen & Appleton, 1977: 32. Richardson, 1989: 45. Herbert, 1991: 11. Herbert & Kilburn, 2004: 219.

Nata liparoxantha — Connolly, 1939: 101, pl. 3, figs 4–6. Richardson, 1989: 46.

Nata minor — Connolly, 1939: 100, pl. 2, figs 9–11. Richardson, 1989: 46.

Helix (Nata) liparoxantha — Bruggen, 1967: 29 [syn. nov. of Nata vernicosa ]

Nata caerotera [sic]— Richardson, 1989: 46.

Nata chaplini — Richardson, 1989: 46.

Not Rhytida vernicosa — Binney, 1879: 355 pl. 14, fig. 1. Binney, 1884: 82, pl. 17, fig. L [= Nata dumeticola ].

The taxonomy of Nata vernicosa is complex and confusing. Connolly (1939) provided the first revisionary comment on the species and noted that the E. Cape taxa Helix caenotera Melvill & Ponsonby, 1892 and Natalina chaplini Melvill & Ponsonby, 1894 were inseparable from Nata vernicosa and thus considered them to be junior synonyms thereof. He treated Helix liparoxantha Melvill & Ponsonby, 1892 from KwaZulu-Natal as a distinct species, also referring it to Nata , as had Watson (1934). Connolly observed, however, that although N. liparoxantha attains a slightly larger size and has somewhat weaker axial sculpture than N. vernicosa , it may in fact represent the same species. Pfeiffer’s N. vernicosa var. minor he considered to be another distinct species with a smaller, smoother shell. Subsequently, Bruggen (1967: 29) placed N. liparoxantha in synonymy with N. vernicosa , and later ( Bruggen 1985) suggested that N. vernicosa might be considered a single wide-ranging and conchologically variable species encompassing all the taxa referred to Nata s.s. by Connolly (1939) [see Introduction], noting at the same time that more conchological and anatomical information was needed.

While the availability of additional material has enabled us to establish that Nata s.s. genuinely does encompass several distinct, highly genetically divergent species, circumscription of N. vernicosa itself has proven more difficult. In recent years, as a practical solution, material that was not clearly referable to any of the other species has been identified as N. vernicosa s.l., including N. liparoxantha and N. minor (both sensu Connolly, 1939 ), as for example in Herbert & Kilburn (2004). This, however, includes specimens exhibiting considerable variation in conchological characters, ranging from low, discoidal specimens virtually devoid of axial riblets, to globose-lenticular (deep-whorled) specimens with strong, axial riblets. From an anatomical perspective, this material exhibits no distinctive characters or consistent patterns of variation in either the radula or the distal genitalia that point to there being more than one species involved. Nonetheless, closer scrutiny of the greater amount of material now available has enabled us to identify within N. vernicosa s.l. a separate, consistently smooth-shelled species that is geographically circumscribed and for the most part allopatric. This we describe below as Nata erugata sp. nov. To date, only a single specimen (NMSA W3343, from Mt Sheba, Mpumalanga) of this species has been included in the molecular work (see Fig. 1 ). While this specimen clustered as the most basally divergent individual in the N. vernicosa clade ( Moussalli & Herbert 2016), additional material spanning the full range of the species will need to be included in future studies.

The remaining Nata vernicosa s.l. material, however, continues to be problematic. Although highly variable in conchological features, we have been unable to discern any clear and consistent patterns in shell morphology that do not seem to intergrade. This variation intergrades both across the landscape and often also at individual localities, in an evidently seamless manner and it encompasses the variation exhibited by all the nominal taxa currently considered to be synonyms of N. vernicosa . The extent of this variation, both between and within populations of N. vernicosa , however, emphasises the significance of the morphological consistency underpinning N. erugata sp. nov. If further cryptic species are present within N. vernicosa , the most promising option for their discovery is likely to lie in molecular studies of a phylogeographic nature. Thus even though we have identified a new species amidst the confusion that has long surrounded N. vernicosa s.l., we are still left with a morphologically diverse assemblage that requires further study using additional techniques.

Type material of Helix vernicosa: Connolly (1939) stated that the ‘type’ of Helix vernicosa Krauss, 1848 was in the Stuttgart Museum and gave its dimensions as ‘diam. 14.8 x 12.0; alt. 7.6 mm’. Krauss, however, gave the dimensions as ‘diam. 5 x 4, alt. 3.3 lines’ (=11.28 x 9.02, alt. 7.44 mm)1. The Stuttgart specimen which Connolly considered to be the type was thus both significantly larger and more depressed than the material seen by Krauss (H:Dmax = 0.514 vs. 0.660). Connolly’s reason for considering this to be the type was not stated and evidently it was an unjustified assumption.

In the SMNH, which contains much original Wahlberg material, there is a lot containing four specimens that Herbert & Warén (1999) treated as possible paralectotypes of Helix vernicosa ( SMNH 4965), believing Connolly’s discussion of ‘the type’ to constitute a lectotype designation. Since the latter was evidently unjustified on the grounds of the specimen’s dimensions and proportions, the type status of the SMNH specimens needs to be reevaluated. The largest specimen is again larger and more depressed than the Krauss material (max. diameter 13.3 mm; H:Dmax 0.586) and thus unlikely to have been seen by Krauss. However, in his remarks following the Latin description of Helix vernicosa, Krauss stated that ‘the largest specimens were more costulate than the younger and as a result slightly semi-gloss.….the ribs are rather sharply raised and close-set…..’, and these comments apply well to the three remaining specimens in this SMNH lot. The two largest of these have crisp, close-set riblets and are lustreless, while the third one is smaller (younger) and has weaker riblets and is more glossy. These two larger lustreless specimens are relatively deep-whorled shells, the proportions of which fit well with measurements given by Krauss and with his original illustration [H:Dmax 0.676 and 0.670 compared with 0.660 for Krauss’s dimensions and 0.659 for his figure]. They are somewhat smaller than the measurements given by Krauss (Dmax 10.2 and 9.7, compared with 11.28 given by Krauss, but a difference of ±10% for the larger of the two is perhaps an acceptable error margin, allowing for differences in measuring methods.

The remaining smaller, more glossy shell ( Fig. 24 M– O) fits Pfeiffer’s description ‘ costulis superficiei obsoletioribus ’ for his variety β. minor (Pfeiffer 1853) , since its sculpture is very much weaker than in the other specimens. It was redescribed in more detail and figured by Connolly (1939) and Herbert & Warén (1999) considered that it may justifiably be considered the lectotype for Pfeiffer’s variety minor .

Since it is important to clarify which taxon is actually represented by the name Helix vernicosa (see below), it is necessary that a lectotype be designated. In light of the above observations, we select the larger of the two deepshelled, strongly ribbed specimens as the lectotype ( Fig. 24 A–C). It was collected by Wahlberg in Natal, its dimensions and proportions are similar to those cited in the original description, it closely resembles the original figure and it matches the additional descriptive comments provided by Krauss.

Type material of synonyms: Lectotype of Helix (Macrocyclis) caenotera Melvill & Ponsonby, 1892 (designated Connolly 1912: 92) in NHMUK (1911.8.8.8) ( Fig. 24 G–I), diameter 17.0 mm (the original description mentioned six specimens, but the whereabouts of the other five is not known). Lectotype of Helix (Macrocyclis) liparoxantha Melvill & Ponsonby, 1892 (designated Connolly 1912: 96) in NHMUK (1911.8.8.7) ( Fig. 24 D–F), diameter 18.0 mm; the original description mentioned four specimens, thus three paralectotypes may also exist, two of these may be specimens in the Melvill-Tomlin Collection ( NMW.1958.158) collected by H.C. Burnup in Port Shepstone [Rowson pers. comm., xii/2015]. Lectotype of Natalina chaplini Melvill & Ponsonby, 1894 (designated Connolly 1912: 92) in NHMUK (1911.8.8.9) ( Fig. 24 J–L), diameter 10.4 mm, label gives locality as 'Cape Colony', but original description states 'Karnachs, near Port Elizabeth (J. Crawford)', (the original description mentioned three specimens, but the whereabouts of the other two is not known).

1. In the foreword to Krauss (1848) he stated that the measurements given were in ‘Pariser Zollen und linien’. [1.0 Paris ligne = 2.256 mm].

Figures

FIGURE 1. Phylogenetic estimate using BEAST uncorrelated (lognormal) relaxed clock model based on two nuclear and two mitochondrial genes (modified from Moussalli & Herbert 2016). A biogeographic calibration was applied to the base of the Rhytididae, representing the East – West Gondwana split (approx. 120 Mya). Nodal support represents posterior probabilities (only PP ≥ 0.90 shown) followed by likelihood bootstrap support (only BS ≥ 75 shown). Images are reflective of size, but not accurately to scale.

FIGURE 24. Type material of Nata vernicosa and synonyms. A – C, Helix vernicosa Krauss, 1848, lectotype (here designated), diameter 10.2 mm (SMNH 4965). D – F, Helix (Macrocyclis) liparoxantha Melvill & Ponsonby, 1892, lectotype, diameter 18.0 mm (NHMUK 1911.8.8.7). G – I, Helix (Macrocyclis) caenotera Melvill & Ponsonby, 1892, lectotype, diameter 17.0 mm (NHMUK 1911.8.8.8). J – L, Natalina chaplini Melvill & Ponsonby, 1894, lectotype, diameter 10.4 mm (NHMUK 1911.8.8.9). M – O, Helix vernicosa var. minor Pfeiffer, 1853, lectotype, diameter 8.0 mm (SMNH 4965).