Nata tarachodes Connolly 1912
Creators: name: David G. Herbert
name: Adnan Mousalli
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Pulmonata
Rhytididae
Nata
Nata tarachodes

description: Nata tarachodes (Connolly, 1912)
Figures 4 D, 5B, 6D, 7B, 8A, 9A, 19–23
? Helix vernicosa [non Krauss, 1848]— Benson, 1850: 254.
Natalina tarachodes Connolly, 1912: 96, pl. 2, fig. 4. Type loc.: Cape Peninsula (generally distributed).
Macrocycloides cosmia [non Pfeiffer, 1852]— Thiele, 1931: 725, fig. 765.
Nata tarachodes — Watson, 1934: 158, 161, pl. 19, figs 6–8. Connolly, 1939: 102. Bruggen, 1970a: 468. Richardson, 1989: 45. Schileyko, 2000: 747, fig. 973A, B.
Etymology. From tarache (Gr.)–disturbance, confusion; presumably referring to the fact that the species was previously confused with Nata vernicosa.
Type material. Holotype (Fig. 19 A–C) in NHMUK (1912.4.27.14), diameter 7.2 mm (8.0 mm fide Connolly 1939), plus five paratypes (1937.12.30.1346–51).
Additional material examined and literature records: See Appendix 2.
Identification. Characterised by its small size, thin shell, low spire, relatively rapidly expanding whorls, and glossy, almost uniformly coloured shell with distinct but rather uneven axial riblets.
Shell (Fig. 19): Lenticular to discoidal, thin, spire low; largest specimens comprising 2.5–2.75 teleoconch whorls; whorls expanding relatively rapidly; periphery close to mid-whorl; suture well above periphery. Protoconch 0.90–1.15 mm in diameter, comprising ±1.0 whorl, smooth and glossy, junction with teleoconch usually distinct. Apical surface of teleoconch sculptured with close-set, axial riblets of uneven strength, often with additional growth scars; riblets evanesce at periphery and base smoother, sculptured by irregular growth-lines. Aperture subcircular to ovate, but peristome interrupted by bulging parietal region; outer lip thin with membranous periostracal fringe; base and umbilical margin evenly rounded; umbilicus moderately wide; columella lip not reflected.
Shell glossy throughout, translucent with honey-gold periostracum when fresh; pigmentation of underlying tissue clearly visible.
Dimensions: Largest specimen, diameter 12.6 mm, height 6.6 mm, but diameter mostly <10 mm; H:D of adults 0.51–0.63 [N=17].
Living animal (Figs 4 D, 20): Body colour rather variable; head and neck grey to dark bluish-grey, often with some microscopic orange pigment granules; tentacles of similar colour, darker toward the tip; foot paler ventrally; tail of foot short, commonly greyish white; skin texture relatively smooth; mantle edge yellowish-grey, with a broad, dark subterminal band; lining of mantle cavity with irregular blackish markings (particularly dense in specimens from the Gansbaai area), the kidney showing through as a whitish trigonal structure (Fig. 20 B). Some populations (e.g. in the forests of the Riviersonderendberge) with tail and mantle edge conspicuously orange (Fig. 20 A).
Radula (Figs 6 D, 21): Formula 0+(7–9)+(4–5); length up to 6.0 mm, with 29–35 V-shaped rows of teeth; teeth progressively larger from anterior to posterior of radula, with up to 10 rows/mm anteriorly, approx. 5 rows/mm posteriorly; largest lateral tooth increasing up to 100% in size; rachidian absent; lateral teeth progressively larger moving away from mid-line, one tooth clearly the largest (fang tooth), this taken to be outermost lateral (tooth n o 7, 8 or 9, may differ on left and right side of radula); inner lateral teeth elongate-lanceolate, fang tooth robust, narrowly trigonal, with slightly in-curved tip giving it a blade-like profile; 4–5 teeth (marginals) beyond largest lateral, the first only slightly shorter than largest lateral, but more slender, remaining marginals decreasing rapidly in size, the outer one minute.
Distal genitalia (Figs 7 B, 8A, 22): Genital pore ventral to pneumostome; right optic tentacle retractor passing to left of penis. Penis relatively short and stout (length ± 2.5 mm), narrowing basally; its wall not conspicuously muscular and lined internally with relatively coarse (stout), close-set papillae (Fig. 8A shows these in the everted state); epiphallus pore surrounded by a slightly raised lip, but not forming an enlarged papilla or verge. Penial retractor muscle attached at apex of penis; epiphallus distinct and comparatively large, ±0.75 length of penis, adnate to side of penis and inserting just below its apex; epiphallus internally papillate, papillae somewhat smaller than those of penis and aligned longitudinally; vas deferens running beside free oviduct before joining spermoviduct. Genital atrium simple and vagina almost non-existent, the free oviduct and bursa copulatrix duct seeming to arise directly from atrium. Bursa copulatrix and its duct about one-third to half length of spermoviduct, basal portion of duct markedly swollen, lined internally with well-developed longitudinal folds, often visible by transparency; duct narrowing distally toward bursa copulatrix; bursa itself ovate, thin-walled and of rather variable size. Genital atrium with a lateral diverticulum arising near base of bursa duct; diverticulum of variable size, well developed in some specimens, but little more than a small pouch in others; internally papillate. [This structure was termed a vaginal appendix by Watson (1934), but a vagina per se is hard to delimit and in the material examined herein the diverticulum appears to derive from the genital atrium, close to the base of the bursa duct.]
Distribution (Fig. 23): Probably endemic to the south-western Cape, from the southern Swartland (Kasteelberg) south to the Cape Peninsula and east to the central Langeberge. Literature records (Connolly 1939) from further east (E. Cape and Lesotho, see Appendix 2) must be considered dubious. It seems probable that these represent misidentified specimens.
Habitat. Occurs in a wide variety of habitats, ranging from fynbos to forest and from the coast to 1500 m in the western Riviersonderendberge (Jonaskop); usually found in accumulations of plant debris beneath shrubs and in forest floor leaf-litter.
Remarks. On the Cape Peninsula the range of Nata tarachodes overlaps with that of Nata dumeticola (see Remarks thereunder), but that species has a deeper shell with stronger, more regular axial riblets, and is usually larger (diameter up to 14.3 mm).
The radula of Nata tarachodes is clearly similar to that of Nata vernicosa, but the distal reproductive tract differs noticeably, particularly with regard to the proportionally larger epiphallus which inserts laterally near the apex of the penis (rather than some distance below the penis apex), and the presence of an atrial diverticulum near the base of the bursa copulatrix duct. A specimen has been observed feeding on a much larger species of Trachycystis in the Koegelberg Nature Reserve (W. Sirgel, in lit., vii/2012).
In addition to the material discussed above, there are three further samples (locality details below) that we initially identified as Nata tarachodes, based on conchological features, but which exhibit unusual radula characters for this species. Firstly a specimen from Newlands Forest [beside contour path, at beginning of Newlands Ravine pathway (33.9628°S: 18.43902°E), 360 m, under logs, D. Raharinjanahary, 10/xii/2006 (NMSA W6601)] is unusual in that the radula formula is 0+6+7, i.e. there are fewer lateral teeth and more marginal teeth than is usual for this species, to such an extent that the number of marginals exceeds the number of laterals. Furthermore, the sequence data for this specimen shows its relationship to other Nata tarachodes material to be rather distant and weakly supported (Moussalli & Herbert 2016).
Secondly, two samples from the Klein Karoo [Calitzdorp area, Matjiesvlei (33.44525°S: 21.65388°E), 360 m, rocky hillside with succulents and aloes, D. Herbert, L. Davis, M. & K. Cole, 04/xi/2013 (NMSA W9588); Gamkaberg Nat. Res., Tierkloof (33.69003°S: 21.90158°E), 440 m, in leaf-litter beneath trees and shrubs, D. Herbert, L. Davis, M. & K. Cole, 07/xi/2013 (NMSA W9548)] are geographically distant from the remaining Nata tarachodes material (localities marked with? in Fig. 23), though the distance is not great and a range extension of this magnitude would not in itself seem unlikely. However, in this material the radula possesses a rachidian tooth [formula: 1+(9–11)+(4–5)] and the number of laterals is larger than is usual for Nata tarachodes. These features render the specimens distinct from typical Nata tarachodes and they are thus questionably referable to the species. Unfortunately the individuals were immature and the distal genitalia were not sufficiently well developed to permit comparison. As yet no molecular data is available for this material.
In both of these cases, definitive conclusions regarding the affinity of the specimens with Nata tarachodes (or otherwise) must await additional sampling and additional comparative data. The possibility exists that one or both may represent unrecognised cryptic species of Nata.
Conservation. Although restricted to the south-western Cape, Nata tarachodes is evidently catholic in its habitat preferences and may be locally common. It is recorded from a number of national parks and nature reserves that span much of its range. Its conservation is thus currently not an issue of concern.
description: Published as part of 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, pp. 1-67 in Zootaxa 4094 (1) on pages 28-32, DOI: 10.11646/zootaxa.4094.1.1, http://zenodo.org/record/266544