Nata watsoni, David G. Herbert & Adnan Mousalli, 2016

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 : 44-49

Nata watsoni sp. nov.

Figures 4 E, F, 6E, 8C, 33–36

Etymology. Named after Hugh Watson (1885–1959), who first drew attention to the unusual radula of this species in 1934 (obituaries: Salisbury 1959; Verdcourt 1960).

Type material. Holotype ( Fig. 25 A–C): SOUTH AFRICA: E. CAPE: Somerset East, Glen Avon Falls, immediately upstream of waterfall (32.6804°S: 25.63437°E), 1130 m, found in crevice on shaded (northern) cliffs beside river, D. Herbert, M. Bursey & G. Redman, 20/i/2002 ( NMSA W6266/T2299).

Paratypes: SOUTH AFRICA: E. CAPE: same data as holotype ( NMSA V9819/T2273, one specimen); Graaff- Reinet, Camdeboo National Park, Valley of Desolation view site (32.26585°S: 24.49203°E), 1350 m, in deep shaded gulley between dolerite cliffs, found feeding on Sheldonia asthenes (Melvill & Ponsonby, 1907) , D. Herbert, L. Davis & M. Cole, 14/iii/2008 ( NMSA W6091/T2303, one specimen); Hankey, Sarah Bartmann municipal grounds (33.83834°S: 24.88594°E), 75 m, thicket, in leaf-litter and under fallen aloes, D. Herbert, L. Davis & M. Cole, st’n 08-050, 21/ix/2008 (W6524/T3921, three specimens); Somerset East, environs of Glen Avon Falls, ca. 0.5 km upstream of waterfall (32.67735°S: 25.6277°E), riverine woodland, in leaf-litter, D. Herbert, M. Bursey & G. Redman, 20/i/2002 ( NMSA V9821/T2274, one specimen); Somerset East, Glen Avon, ‘The Gorge’ (32.67733°S: 25.62767), M. Bursey, 22/ix/2002 ( ELM D13640, one specimen); Somerset East, slopes of Bosberg (32.70257°S: 25.57605°E), indigenous woodland, in leaf-litter, D. Herbert, M. Bursey & G. Redman, 22/i/2002 ( NMSA V9789/T2297, one specimen); Kuzuko Game Res. (33.198°S: 25.487°E), thicket beside small dry water course, D. Herbert, L. Davis & M. Cole, 08/iii/2008 ( NMSA W6022/T2296, one specimen); Kuzuko Game Res. (33.16804°S: 25.46650°E), Acacia karoo thicket beside water course, D. Herbert, L. Davis & M. Cole, 09/iii/2008 ( NMSA W6029/T2298, 16 specimens); Grahamstown area, Riebeek East, Teafontein Farm (33.22975°S: 26.25088°E), Aloe ferox veld with bush clumps, in leaf-litter and under fallen aloes, D. Herbert, L. Davis & M. Bursey, 10/iii/2007 ( ELM D15163, two specimens; NHMUK 20080531, one specimen; NMSA W5189/T2272, three specimens; NMW.Z.2008.039.00001, one specimen; RMNH.MOL.109.752, one specimen); Grahamstown, Mountain Drive (33.32834°S: 26.50260°E), indigenous forest, under log, A. Moussalli & D. Stuart- Fox, 3/xii/2005 ( NMSA W4199/T2275, one specimen); Alexandria Forest (33.7213°S: 26.415°E), R.F. Lawrence, i/1964 ( NMSA V5204/T2305, one specimen).

Additional material examined: See Appendix 5.

Identification. The shell of N. watsoni sp. nov. closely resembles that of N. erugata sp. nov. and N. vernicosa . The latter differs in possessing fine, close-set axial riblets on the adapical surface, but both N. watsoni sp. nov. and N. erugata sp. nov. share the same almost smooth, highly glossy shell, sculptured solely by growth-lines. Compared to N. erugata sp. nov., the shell of N. watsoni sp. nov. is smaller (max. diameter 16 mm vs. 21 mm), its spire usually less prominent and the umbilicus somewhat narrower, but definitive separation of the two requires examination of the radula, which has finer, much more numerous teeth in N. watsoni sp. nov. The distributions of the two species do not overlap, which aids in determining the likely identity of empty shells.

Shell ( Fig. 33 ): Lenticular to discoidal; spire very low; with up to 3.0 teleoconch whorls, exceptionally up to 3.75 whorls (holotype); suture well above periphery, last adult whorl descending slightly prior to aperture only in the largest specimens and even then remaining well above periphery. Protoconch small, diameter 1.03–1.42 mm, comprising ± 1.25 whorls, but junction with teleoconch often not clear; smooth and glossy. Teleoconch weakly sculptured, lacking axial riblets, but with faint, relatively widely spaced subsutural pleats and occasional stronger growth-lines or scars; surface glossy. Aperture subcircular when young, becoming more oblique with growth; peristome interrupted by parietal region which bulges into aperture; outer lip thin with membranous periostracal fringe when undamaged; base and umbilical margin evenly rounded; umbilicus relatively narrow, steep-sided; columella lip scarcely if at all reflected.

Shell glossy, periostracum relatively uniform pale yellowish-brown, but with occasional indistinct, slightly darker, golden-brown axial bands.

Dimensions: Holotype (=largest specimen) diameter 16.0 mm, height 8.25 mm; H:D 0.49–0.59; few specimens with diameter>11.0 mm.

Living animal ( Fig. 4 E, F): Coloration of head foot variable; head and neck commonly orange-brown to brown ( Fig. 4 E), darker dorsally, paler and more greyish beneath shell and posteriorly, pedal margin sometimes deeper orange, tentacles grey to dark grey; one specimen more uniformly pale cream-buff with greyish tentacles ( Fig. 4 F). Neck region capable of great elongation; skin in this region relatively strongly textured; in occasional specimens skin tubercles may be darker than intervening grooves. Lung wall variously flecked with conspicuous black spots and blotches, sometimes heavily so ( Fig. 4 E); mantle edge with pinkish or orange tinge, no blue coloration evident in vicinity of pneumostome; lower left mantle lobe with a narrow base and alate extensions on both sides.

Radula ( Figs 6 E, 34): Highly distinctive; formula 0+(20–33); length up to 13 mm, with 42–60 transverse rows of teeth; rows acutely V-shaped in central area with a distinct mid-line diastema (perhaps an artefact of preparation), rows broadening laterally and sometimes recurved at margin; number of transverse rows and number of teeth per row related to size of animal, 4–6 rows/mm in large individuals (shell diameter> 12 mm), over 10 rows/ mm in smaller ones. Rachidian absent; no one tooth in each half-row is clearly the largest and thus a cut-off between lateral and marginal series cannot be identified; inner series of teeth well developed, elongate and aculeate, sometimes weakly curved or sinuous ( Fig. 34 C); increasing slightly in size from first to 6–8; outer series decreasing in size somewhat more noticeably, but still gradually; teeth at radula margin considerably smaller, with a trigonal base-plate and very slender, sharply pointed cusp ( Fig. 34 B, D).

Distal genitalia ( Fig. 35 ): Genital pore ventral to pneumostome; right optic tentacle retractor passing to left of penis. Penis relatively long and slender (length 5.5–8.0 mm), somewhat constricted at its junction with genital atrium and in mid region; retractor muscle attached apically; epiphallus inserts laterally, approximately one-quarter length of penis from its apex; penis lumen lined by very fine, close-set papillae; epiphallus pore surrounded by an oval-shaped complex of ridges (considerable individual variation evident in pattern), this more extensive basal to pore; 1–2 well-developed longitudinal ridges present on lumen wall opposite epiphallus pore. Epiphallus short, its lumen lined with longitudinal rows of papillae, somewhat coarser than those in penis; vas deferens narrow, passing down penis (sometimes sinuously so), reflexing around angle between penis and vagina, and then running alongside free oviduct to join base of spermoviduct.

Genital atrium simple, cylindrical; vagina short, base of bursa duct connected to body wall by muscle fibres; free oviduct short, basal part of spermoviduct comprising oviductal tissue only, prostatic portion present only in upper half to two-thirds, vas deferens continuing thereafter on oviduct surface; spermoviduct sinuous and with superficial folds in oviductal portion. Bursa copulatrix duct somewhat broader basally, narrowing at about onethird its length then broadening during the mid and upper portion before narrowing again prior to the bursa itself (thus reminiscent of the penis shape); bursa pyriform to elongate ovate.

Distribution ( Fig. 36 ): Endemic to E. Cape, South Africa; primarily in the lower catchments of the Gamtoos, Sundays and Great Fish rivers, but extending inland to Graaff-Reinet; from the coastal hinterland to 1350 m.

Habitat. Largely restricted to areas falling within the broader confines of the Albany Thicket Biome ( Mucina & Rutherford 2006), but occurring in a relatively wide variety of habitats within this, from southern coastal forest to fragments of southern mistbelt forest in shaded gorges and gullies, as well as low, open thicket. Lives in leaflitter beneath bushes, under logs, stones and fallen aloes, and in rocky crevices.

Remarks. Two existing names are available for moderately sized Nata specimens from the Albany Thicket, N. caenotera (Melvill & Ponsonby, 1892) and N. chaplini ( Melvill & Ponsonby, 1894) . However, the types of both of these taxa ( Fig. 24 G–I and J–L, respectively) have distinct axial riblets and they are thus not applicable to the present material. We treat both as junior synonyms of N. vernicosa .

As discussed in the above identification section, N. watsoni sp. nov. is chiefly comparable with N. erugata sp. nov. and N. vernicosa . Although its shell exhibits no truly characteristic features, its radula is highly distinctive, having finer and much more numerous teeth. In addition to the differences in its radula morphology, N. watsoni sp. nov. also possesses features of the distal genitalia that distinguish it from N. erugata sp. nov. and N. vernicosa . These include the dumbbell shape of the penis, the more elaborate pattern of ridges on the inner penis wall associated with the epiphallus pore and the finer papillae lining the lumen. The bursa copulatrix duct is also not as obviously swollen basally and there is a constriction at approximately one-third of its length, mirroring the constriction in the penis. In addition, the prostatic portion of the spermoviduct is distinctly shorter than the oviductal portion, and the vas deferens initially passes over the folded lobes of the oviduct.

The marked variation in body colour exhibited by this species is surprising ( Fig. 4 E, F), but the specimens concerned consistently show the same distinctive features of radula and genital morphology. The distribution of N. vernicosa overlaps extensively with that of N. watsoni sp. nov., particularly near the coast, and in places the two have been found at the same locality. A specimen from Graaff-Reinet was found feeding on the urocyclid Sheldonia asthenes (Melvill & Ponsonby, 1907) , indicating that despite its unusual radula morphology, the species still feeds on other molluscs.

Conservation. Although endemic to E. Cape and the Albany Thicket Biome, Nata watsoni sp. nov. is not a rare species and it has relatively broad habitat preferences. In places it may be locally common and it is recorded from a number of sites within the Greater Addo Elephant National Park, as well as the Camdeboo National Park and various municipal and local authority conservation areas. Its conservation is thus currently not an issue of concern, though its status as a provincial endemic is noteworthy.

Figures

FIGURE 4. Living animals of Nata and Natella. A, Nata aequiplicata sp. nov., holotype, Stinkhoutkloof, E. Cape, shell diameter 6.5 mm (NMSA W 9248 / T 3066). B, Nata dumeticola, West Coast National Park, W. Cape, shell diameter 10.8 mm (NMSA W 3224). C, Nata erugata sp. nov., Tullach-Mohr, Nelspruit area, Mpumalanga, shell diameter 20 mm (MV ex NMSA W 3301). D, Nata tarachodes, Grootbos Private Nat. Res., Gansbaai, W. Cape, shell diameter 7.7 mm (NMSA W 5658). E, Nata watsoni sp. nov., Hankey, E. Cape, shell diameter 7.5 mm (paratype NMSA W 6524 / T 3921). F, Nata watsoni sp. nov. Camdeboo National Park, Graaff-Reinet, E. Cape, shell diameter 13.0 mm (paratype, NMSA W 6091 / T 2303). G, Nata vernicosa, Vernon Crookes Nat. Res., KwaZulu-Natal, shell diameter 14.0 mm (NMSA W 8020). H, Natella viridescens, Ithala Game Res., KwaZulu-Natal, shell diameter 3.7 mm (NMSA W 7263).

FIGURE 6. Radulae of Nata and Natella, automontage light micrographs of half-row portions of stained radula mounts. A, Nata aequiplicata sp. nov., type locality (paratype, NMSA W 9249 / T 3067). B, Nata dumeticola, Jacobsbaai, W. Cape (NMSA V 7760). C, Nata erugata sp. nov., Golden Gate Highlands National Park, Free State (paratype, NMSA W 4243 / T 3913). D, Nata tarachodes, Oubos, W. Cape (NMSA W 5671). E, Nata watsoni sp. nov., Graaff-Reinet, E. Cape (paratype, NMSA W 6091 / T 2303). F, Natella viridescens, Ithala Game Res., KwaZulu-Natal (NMSA V 2530). Scale bars: A = 100 µm; B = 200 µm; C – E = 250 µm; F = 50 µm.

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).

FIGURE 25. Nata vernicosa (Krauss, 1848). A – C, large typical specimen with strong sculpture, Mbotyi, E. Cape, diameter 20.7 mm (NMSA W 4119). D – F, large low-spired, weakly sculptured, glossy specimen, liparoxantha morph, Umtamvuna Nat. Res., KwaZulu-Natal, diameter 19.5 mm (NMSA W 7901). G – I, strongly sculptured, deep-whorled specimen, Kelso, KwaZulu-Natal, diameter 16.3 mm (NMSA W 7940). J – P, additional specimens from throughout the range of the species [J, Lekgalameetse Nat. Res., Limpopo, diameter 20.6 mm (NMSA V 5544). K, Mount Sheba, Mpumalanga diameter 16.0 mm (NMSA W 3344). L, Hluhluwe Game Res., KwaZulu-Natal, diameter 21.7 mm (NMSA V 571). M, Grahamstown, E. Cape, diameter 15.3 mm (NMSA W 4198). N, Van Stadens Wild Flower Res., E. Cape, diameter 15.5 mm (NMSA W 8359). O, Ferndale, E. Cape, diameter 14.0 mm (NMSA W 8436). P, Fig Tree, Addo Elephant Park, E. Cape, diameter 15.9 mm (NMSA W 4221)].

FIGURE 33. Nata watsoni sp. nov. A – C, holotype, Glen Avon Falls, Somerset East, E. Cape, diameter 16.0 mm (NMSA W 6266 / T 2299). D – F, low-spired juvenile, Riebeek East, Grahamstown, diameter 10.5 mm (paratype, NMSA W 5189 / T 2272). G – I, Hankey, diameter 13.6 mm (paratype, NMSA W 6524 / T 3921).

FIGURE 34. Nata watsoni sp. nov., radula. A, entire width of radula. B, recurved rows of teeth at radula margin. C, middle and right side of radula. D, recurved rows of teeth at radula margin. A, B, D, Camdeboo National Park, paratype NMSA W 6091 / T 2303; C, Somerset East, holotype. A, B, stained radula slides; C, D, scanning electron micrographs. Scale bars: A, D = 100 µm; B = 50 µm; C = 250 µm.

FIGURE 35. Nata watsoni sp. nov., genitalia. A, entire genital tract, minus ovotestis, holotype (NMSA W 6266 / T 2299). B, penial complex, paratype (NMSA W 5189 / T 2272). C, longitudinal dissection of penis to show internal structure, holotype. Abbreviations: ag, albumen gland; bc, bursa copulatrix; bd, bursa copulatrix duct; ep, epiphallus; epp, epiphallus pore; ga, genital atrium; hd, hermaphrodite duct; lpr, longitudinal penis ridge; p, penis; pr, penial retractor muscle; sod, spermoviduct; v, vagina; vd, vas deferens.

FIGURE 36. Distribution of Nata watsoni sp. nov. Triangles with a white centre indicate localities for specimens used in DNA analyses (Moussalli & Herbert 2016); contour at 1000 m.