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 : 36-39

publication ID	https://doi.org/ 10.11646/zootaxa.4094.1.1
publication LSID	lsid:zoobank.org:pub:E5F1E766-687D-4B00-974B-8D7939DC66A0
DOI	https://doi.org/10.5281/zenodo.5615854
persistent identifier	https://treatment.plazi.org/id/03E687FC-E02E-D761-FF1A-11FA0FCB9F97
treatment provided by	Plazi
scientific name	Nata vernicosa ( Krauss, 1848 )
status

Treatment

Nata vernicosa ( Krauss, 1848)

Figures 2 View FIGURE 2. A B, 3C, 4G, 5A, 7D, 8B, 9B, 24–29

Etymology. From vernix (L.)—varnish; presumably in reference to the periostracum, which can be glossy and lacquer-like.

Selected locality data for material examined: See Appendix 3.

Identification. The shell characters that most readily distinguish this species from its congeners are its relatively large size and its sculpture of axial riblets (weak or strong). Other species with axial riblets are considerably smaller at adult size, whereas other similarly-sized species are smoother, with a sculpture that primarily comprises growth-lines only. Juveniles can be difficult to identify, but beyond W. Cape N. vernicosa is the only species with axial riblets except for N. aequiplicata sp. nov. That species is very much smaller, has axial sculpture that continues onto the base and into the umbilicus, and is narrowly endemic to a small part of E. Cape.

Shell ( Figs 24 View FIGURE 24 , 25 View FIGURE 25 ): Lenticular to globose-lenticular, proportions very variable (H:D 0.49–0.71), some specimens with depressed whorls and a low spire ( Fig. 25 View FIGURE 25 D), others with deep whorls and a more prominent spire ( Fig. 25 View FIGURE 25 G); largest specimens comprising up to 3.75 teleoconch whorls; periphery at mid-whorl, occasionally somewhat below it ( Fig. 25 View FIGURE 25 O); suture well above periphery, slightly descendant prior to aperture in some large specimens. Protoconch size very variable, diameter 1.1–2.6 mm, comprising ±1.0 whorl, smooth and glossy, junction with teleoconch often ill-defined. Apical surface of teleoconch sculptured with axial riblets, relatively weak in some specimens, crisp and close-set in others; shell commonly glossy, but tending to be lustreless when sculpture stronger ( Fig. 25 View FIGURE 25 A, B, G, H); riblets evanesce at periphery and base smoother, sculptured primarily by uneven growth-lines. Base and umbilical margin evenly rounded; umbilicus of moderate width, steep-sided, with axial riblets usually reappearing to some extent within. Aperture roundly to obliquely ovate; peristome interrupted by bulging parietal region; outer lip thin with membranous periostracal fringe (commonly lost); upper part of columella lip extending forward and a little reflected.

Shell translucent milky-white; periostracum pale straw-brown to pale olive-green, honey-gold or olive-brown, usually with some axial variation in intensity, producing unevenly spaced, slightly darker axial banding.

Dimensions: Largest specimen, diameter 24.5 mm, height 16.1 mm; H:D of adults 0.49–0.71 [N=100].

Living animal ( Figs 4 View FIGURE 4 G, 26): Body colour very variable; head and neck ranging from pale grey ( Fig. 26 View FIGURE 26 C) to brownish-grey ( Fig. 26 View FIGURE 26 A), bluish-grey and even dark charcoal grey ( Fig. 26 View FIGURE 26 B); foot paler ventrally and beneath shell; commonly with some microscopic orange pigment granules, particularly on tail, ventral margins of foot and mantle edge ( Fig. 26 View FIGURE 26 F); tentacles usually a darker shade of body colour. Tail of foot short, narrowly acuminate; skin grooves coarse and well defined in some individuals, less so in others; mantle edge generally pale; lining of mantle cavity mostly lacking black markings, but commonly (perhaps invariably) with a black blotch inset a short distance above pneumostome ( Fig. 26 View FIGURE 26 A, B, D); kidney not clearly visible by transparency. In some populations (e.g. from Ngome Forest, KwaZulu-Natal) orange pigmentation on tail and mantle edge is conspicuous. Freshly preserved specimens frequently with a bluish tinge in pneumostomal area of mantle collar, perhaps related to the presence of underlying mucus glands.

Radula ( Fig. 27 View FIGURE 27 ): Formula 0+(8–11)+(3–4); length up to 15.5 mm, with 23–32 V-shaped rows of teeth in larger specimens (more in smaller ones); teeth progressively larger from anterior to posterior of radula; tooth form essentially similar to that of Nata tarachodes ; rachidian absent; largest tooth, the fang tooth (number 8–11) taken to delineate limit of lateral series; fang tooth elongate-trigonal, with a sharply pointed tip and a substantial base-plate; middle laterals much more slender and narrowly acuminate, the tips sometimes curving inwards. Specimens from KwaZulu-Natal and the Cape usually with 8–9 laterals ( Fig. 27 View FIGURE 27 A), those from Mpumalanga and Limpopo usually, but not invariably, with 10–11 laterals ( Fig. 27 View FIGURE 27 C).

Distal genitalia ( Figs 8 View FIGURE 8. A B, 28): Genital pore ventral to pneumostome; right optic tentacle retractor passing to left of penis. Penis shape variable, ranging from long and slender to clavate or ovate-fusiform, frequently somewhat sinuous; length up to 6.0 mm; penis wall not conspicuously muscular, internally with numerous small papillae arranged in ill-defined radiating ridges around epiphallus pore and sometimes aligned on low longitudinal folds ( Fig. 8 View FIGURE 8. A B shows these in the everted state). Penial retractor muscle attached at apex of penis; epiphallus present, approx. one-third length of penis, inserting laterally; point of insertion variable, between one-third and three-quarters length of penis from its base; vas deferens and epiphallus loosely adnate to side of penis, but not fused to it; vas deferens continues to penis base before running alongside free oviduct to join spermoviduct, frequently sinuous beside free oviduct. Genital atrium simple and vagina short or scarcely evident, the free oviduct and bursa copulatrix duct seeming to arise side-by-side from atrium. Bursa copulatrix and its duct about half length of spermoviduct; basal half to three-quarters of duct broader, subcylindrical, sometimes narrowing slightly prior to insertion into atrium; distal portion of duct narrower and usually somewhat constricted at junction with bursa; broader portion of duct lined internally with numerous fine, close-set, wavy longitudinal folds, these becoming fewer and thicker in narrower section preceding bursa; bursa itself elongate-ovate, thin-walled and small, onequarter or less length of its duct. Length of free oviduct variable; spermoviduct not convoluted, but usually sinuous; oviductal and prostatic portions distinct, the former with superficial folds. Albumen gland reniform, its size related to reproductive state; proximal half of hermaphrodite duct thicker and convoluted; ovotestis comprising approx. six fusiform lobes embedded in apical part of digestive gland.

Distribution ( Fig. 29 View FIGURE 29 ): Widely distributed over much of eastern South Africa, from Mossel Bay in the west, through E. Cape and KwaZulu-Natal, to Mpumalanga, Limpopo and Swaziland; mostly in the coastal hinterland and inland to altitudes of approximately 1000 m, rarely more. However, in the northern part of its range the species is mostly associated with the Soutpansberg, Wolkberg and northernmost Drakensberg escarpment, where it primarily occurs at altitudes of 1000–1750 m. In addition, there is also a population occurring in suburban gardens in the environs of Cape Town, but this is almost certainly derived from translocated individuals.

Habitat. One of the most ecologically tolerant of all South African land snails; occurs in a wide variety of habitats ranging from open savannah, thornveld, coastal scrub and thicket to riverine woodland and dune, coastal scarp and afrotemperate forests, as well as Eucalyptus plantations, and suburban parks and gardens.

Remarks. The considerable variability in shell form exhibited by this species has been mentioned above. Further assessment of this variation needs to be undertaken in conjunction with phylogeographic analysis of molecular data. It is quite possible that additional cryptic species may be found to exist within what we here treat as a single variable entity.

Conservation. As currently interpreted, Nata vernicosa is one of the most widespread and commonly encountered snails in natural habitats in the south-eastern parts of South Africa. It is also tolerant of transformed habitats, particularly suburban gardens where the rather more well-watered conditions are favourable to both it and its prey. The conservation of the species is thus not a matter of concern. It is, however, a species that should be nurtured on account of its potential to reduce introduced pestiferous snail and slug populations.