Nata aequiplicata, 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 : 18-22

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.5615843
persistent identifier	https://treatment.plazi.org/id/03E687FC-E01C-D751-FF1A-167409FB98D0
treatment provided by	Plazi
scientific name	Nata aequiplicata
status	sp. nov.

Treatment

Nata aequiplicata sp. nov.

Figures 4 View FIGURE 4 A, 6A, 7A, 10–13

Etymology. From aequalis (L.)—equal, uniform; and plico (L.)—to fold, plicatus —folded; with reference to the distinctive shell sculpture.

Type material. Holotype ( Fig. 4 View FIGURE 4 A, 10A–C): SOUTH AFRICA: E. CAPE: Loerie area, Longmore, Stinkhoutkloof (33.79940°S: 25.09698°E), 540 m, indigenous forest, under logs, D. Herbert, L. Davis & M. Cole, st’n 12-45, 17/xi/2012 ( NMSA W9248/T3066).

Paratypes: SOUTH AFRICA: E. CAPE: same data as holotype, in leaf-litter and under logs ( NMSA W9249/ T3067, three specimens); Van Stadens Wild Flower Res. (33.91200°S: 25.20507°E), 175 m, gorge forest, in leaflitter, D. Herbert, L. Davis & M. Cole, st’n 08-56, 22/ix/2008 ( ELM D15970/T032, two specimens); ditto (33.91165°S: 25.20465°E), 190 m, indigenous forest on steep rocky slope, in leaf-litter, D. Herbert, L. Davis & M. Cole, st’n 11-21, 27/ix/2011 ( NMSA W8356/T3897, one specimen); Ferndale, near Patensie (33.71642°S: 24.85030), 160 m, riverine woodland, in leaf-litter, D. Herbert, L. Davis & M. Cole, st’n 11-25, 28/ix/2011 ( NMSA W8320/T3898, two specimens).

Other material examined: (all NMSA): SOUTH AFRICA: E. CAPE: Same data as holotype (W9206); Thornhill area, valley of Berg River (33.87457°S: 25.11965°E), 155 m, indigenous forest, in leaf-litter, D. Herbert & L. Davis, st’n 12-44, 17/xi/2012 (W9199); Van Stadens River gorge (33.90937°S: 25.19090°E), 130 m, indigenous forest, in leaf-litter, D. Herbert & L. Davis, st’n 12-42, 16/xi/2012 (W9229); Van Stadens Wild Flower Res. (33.91200°S: 25.20507°E), 175 m, gorge forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, st’n 08-56, 22/ ix/2008 (W6485).

Identification. Shell superficially similar to that of other Nata species, but distinguished by its small size and the evenly plicate axial sculpture that extends around the periphery and into the umbilicus.

Shell ( Fig. 10 View FIGURE 10 ): Discoidal, last adult whorl somewhat tumescent, spire low to almost flat; largest specimens comprising 2.50–2.75 teleoconch whorls; suture well above periphery, not noticeably descendant prior to aperture; periphery slightly below mid-whorl; surface glossy throughout. Protoconch very small, diameter 0.7–0.9 mm, comprising ±1.0 whorl, but junction with teleoconch usually not clear; for the most part smooth and glossy, but developing collabral growth-lines toward junction with teleoconch. Teleoconch relatively strongly sculptured with distinct, evenly spaced, axial pliculae that continue around periphery, onto base and into umbilicus. Aperture roundly ovate; peristome interrupted by bulging parietal region; outer lip thin with membranous periostracal fringe where undamaged, its adapical edge strongly convex in profile; base and umbilical margin evenly rounded; umbilicus relatively narrow and steep-sided, patent to apex; columella lip not reflected.

Translucent, pale corneous brown with distinct, irregularly spaced, darker brown, axial bands when fresh, but colour pattern fading to pale yellowish-buff in dead shells.

Dimensions: Holotype, diameter 6.5 mm, height 3.6 mm; largest specimen, diameter 6.7 mm, height 3.7 mm; H:D of adults 0.535–0.585 (N=6).

Living animal ( Fig. 4 View FIGURE 4 A): Head and neck grey, darker anteriorly and on tentacles; foot paler ventrally and beneath shell; tail of foot relatively short, greyish-white; skin texture fine, somewhat coarser on neck; mantle edge greyish-white; lower left mantle lobe broad with relatively small lateral flanges; lining of mantle cavity not strongly marked but with some dark pigmentation, particularly bordering the pulmonary vein; kidney trigonal, pale buff, not conspicuous through shell.

Radula ( Figs 6 View FIGURE 6 A, 11): Formula 1+(6–7)+(8–10); length up to 4.5 mm, with 37–42 broadly V-shaped rows of teeth; teeth progressively larger from anterior to posterior of radula, approx. 13 rows/mm anteriorly, approx. 7 rows/mm posteriorly; largest lateral tooth increasing up to 45% in size from anterior to posterior of radula; rachidian small, narrowly lanceolate and sharply pointed; innermost laterals small, but distinctly larger than rachidian, subsequent laterals progressively increasing in size, with teeth 5–6 (7 as well toward posterior of radula) much larger; inner laterals lanceolate, teeth 5–7 much broader and more trigonal; marginal series beginning beyond lateral 6–7, progressively decreasing in size, these teeth, 8–10 in number, are initially knife-shaped with a broader base and up-curved tip, but become shorter and more spathulate toward radula margin. Basal attachment of larger teeth L-shaped.

Distal genitalia ( Fig. 12 View FIGURE 12 ): Genital pore ventral to pneumostome; right optic tentacle retractor passing to left of penis. Penis relatively short and stout (length ±2.0 mm), broadest in mid region; its wall not conspicuously muscular, lumen lined with relatively coarse papillae; epiphallus pore simple, subapical. Penial retractor muscle attached at apex of penis; epiphallus present, one-third to half length of penis; adherent to side of penis and inserting subapically; vas deferens continues to penis base before running alongside free oviduct to join spermoviduct. Genital atrium simple and vagina almost non-existent, the free oviduct and bursa copulatrix duct seeming to arise directly from atrium, as does the penis. Atrial wall with indistinct longitudinal folds, becoming stronger near base of free oviduct and bursa copulatrix duct. Bursa copulatrix and its duct about one-quarter to onethird length of spermoviduct; basal portion of duct broader, lined internally with longitudinal folds originating in atrium; duct narrowing in mid region before bursa; bursa itself ovate, thin-walled and approx. half length of its duct. Genital atrium also with a relatively large, globose, lateral diverticulum, similar to but larger than that adjacent to base of bursa duct in Nata tarachodes ; diverticulum with a prominent internal pleat forming a raised Ushaped ridge extending from close to genital pore, into diverticulum and ending adjacent to origin of bursa duct; crest of ridge bearing irregular transverse folds.

Distribution ( Fig. 13 View FIGURE 13 ): Known only from E. Cape, South Africa; evidently a restricted-range endemic, confined to a small area of the coastal hinterland between Jeffreys Bay and the eastern limit of the Cape Fold Mountains (Elandsberge); 130– 540 m.

Habitat. Southern Coastal Forest in the Van Stadens River gorge and Southern Temperate Forest further inland on the south-facing portion of the Elandsberge ( Mucina & Rutherford 2006); living in leaf-litter and under logs.

Remarks. Nata aequiplicata sp. nov. is one of the smallest species of Nata , but it is relatively easily distinguished on account of its strong, regularly and quite widely spaced axial pliculae and the fact that this axial sculpture extends around the periphery and into the umbilicus. The colour pattern of living individuals is also bolder than all except occasional specimens of Nata vernicosa . It is unusual in that the radula retains a rachidian tooth, as does that of Natella viridescens . The reproductive system, however, is similar to that of Nata tarachodes , and molecular data group the species with Nata s.s. ( Moussalli & Herbert 2016).

An additional juvenile specimen from Hogsback, E. Cape, included in our molecular phylogeny clustered together with the present species. However, no voucher shell or soft parts are available and it is not possible to establish whether it is morphologically referable to Nata aequiplicata sp. nov. Further targeted field work in the Hogsback area has not brought to light any material resembling Nata aequiplicata sp. nov. suggesting that this specimen may represent a distinct entity requiring further investigation.

Conservation. Although Nata aequiplicata sp. nov. is small and thus easily overlooked, the E. Cape of South Africa is a relatively well-collected region and the absence of records of the species from much of the province suggests that its distribution is genuinely restricted to a small area in the south-west of the province. Further survey work is needed, particularly in forest habitats on the south facing slopes of the mountains of the eastern Cape Fold Belt, to establish whether the species ranges further to the west. The data currently available indicate that this is a species of conservation concern, for which the preservation of indigenous forests in the area between the Gamtoos River valley and Port Elizabeth is likely to be critical.