Nata dumeticola (David G. Herbert & Adnan Mousalli 2016)
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- Nata dumeticola David G. Herbert, 2016, Zootaxa 4094: 24-27.
Etymology. From dumetum (L.)–a thicket, dumeticola –thicket dweller; with reference to its coastal scrub habitat.
Type material. Three probable syntypes in NHMUK (19126.96.36.199– 8), labelled ‘S. Africa’ ‘Benson’s types’. Connolly’s statement ‘ type in British Museum’ (Connolly 1912: 93, repeated 1939: 102) does not constitute a lectotype designation as no one individual was clearly specified. The largest of the three is here illustrated (Fig. 15 A–C) and designated as the lectotype (diameter 11.4 mm). Additional material examined and literature records: See Appendix 1. Identification. The relatively strong, crisp and close-set axial riblets on the adapical surface, combined with the rather globose profile of adult specimens renders this species distinctive. Juveniles and subadults may resemble N. aequiplicata sp. nov., but in that species the axial riblets are more widely spaced and remain distinct on the base, and its protoconch is considerably smaller. N. tarachodes has more rapidly expanding whorls, less regular axial sculpture and is more depressed.
Shell (Fig. 15): Lenticular to sub-globose, spire frequently relatively elevated; largest specimens comprising ± 3.25 teleoconch whorls; periphery close to mid-whorl in small specimens (diameter <10.0 mm) but usually well below mid-whorl in the largest individuals; suture just above periphery, slightly descendant prior to aperture in some large specimens. Protoconch 1.6 –2.0 mm in diameter, comprising ±1.0 whorl, smooth and glossy, junction with teleoconch usually evident. Apical surface of teleoconch sculptured with distinct, close-set, axial riblets; riblets evanesce at periphery and base smoother, sculptured primarily by uneven growth-lines. Aperture roundly ovate; peristome interrupted by bulging parietal region; outer lip thin with membranous periostracal fringe (commonly lost); base and umbilical margin evenly rounded; umbilicus relatively narrow and steep-sided, particularly in large individuals; columella lip weakly reflected, but only in large specimens Shell translucent milky-white; periostracum semi-matt to glossy, straw-yellow to olive-brown or tan, usually with some slight axial variation in intensity. Dimensions: Largest specimen, diameter 14.3 mm, height 9.1 mm; H:D of adults 0.57–0.78 [N= 22]. Living animal (Fig. 4 B): Head-foot pale grey, neck region with relatively coarse, darker grey skin granules; longitudinal mid-line grooves somewhat fragmented by granulation; optic tentacles smooth, with dark grey retractor muscles (data from one individual).
Radula (Figs 6 B, 16): Formula 0+(14–22); length up to 5.7 mm, with approx. 55 broadly V-shaped rows of teeth; no obvious distinction between lateral and marginal series; teeth progressively increasing in length and width, then decreasing in size, and more rapidly so toward radula margin; inner teeth with curved, claw-like cusp; subsequent mid-series teeth progressively larger, broader and more quadrate with a curved outer cutting edge, sometimes leading to an ill-defined apical cusp; outer teeth progressively smaller, lanceolate to spathulate, the outermost one minute.
Teeth at anterior of radula smaller and more numerous, becoming fewer and larger toward posterior. In one specimen, near the anterior of the radula (juvenile portion) the largest teeth in each half-row were numbers 13–15 (of 22), in the mid region numbers 8–10 (of 18) and in the posterior third numbers 6–8 (of 15). The dentition thus becomes coarser and more robust as the animal grows. Watson (1934) has pointed out that the radula illustrated by Binney (1879, 1884) as that of Nata vernicosa was certainly not correctly identified and in all probability belonged to a specimen of Nata dumeticola, although puzzlingly his figure did not show the L-shaped basal attachment of the larger teeth (Fig. 6 B), probably due to the use of different staining methods. Distal genitalia (Fig. 17): Genital pore situated approx. midway between pneumostome and tentacles; right optic tentacle retractor passing to left of penis. Penis of moderate length (± 2.7 mm), broadest in apical half with basal region conspicuously narrow in some specimens; insertion of epiphallus lateral, approx. one-third length of penis from its apex; interior of penis with a raised pilaster overlying adnate epiphallus; an elongate subapical pore opens on pilaster crest; pore with lobate lips; interior of pore with a second set of lips surrounding narrowly elongate opening of epiphallus; remainder of swollen apical half of penis lumen covered with micropapillae; basal half of penis with fine, ill-defined longitudinal folds. Penial retractor muscle attached at apex of penis; epiphallus one-third to half length of penis; vas deferens passes down to penis base and then runs somewhat sinuously 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 upper part of atrium. Bursa copulatrix and its duct about three-quarters length of spermoviduct, basal half of duct swollen, lined internally with ill-defined longitudinal folds, distal half narrow; bursa copulatrix itself ovate, thin-walled.
Distribution (Fig. 18): Known primarily from the coastal hinterland along the Atlantic Cape coast, from St Helena Bay south to the Cape Peninsula and north-western shores of False Bay. An additional record from Garies in Namaqualand (SAMC A 7719), though not impossible, is substantially further to the north and requires confirmation. Habitat. Coastal scrub and fynbos; in sandy soil and accumulations of plant debris beneath shrubs and bushes.
Remarks. A variable species in terms of shell proportions. Juvenile and subadult specimens are relatively low and lenticular (Fig. 15 G, J), but in larger individuals the last adult whorl is considerably deeper and its periphery usually situated well below mid-whorl, giving the shell a more elevated and more globose form (Fig. 15 A, H, I). Nata dumeticola is the only rhytidid occurring on the Atlantic Cape coast north of Table Mountain and the Cape Peninsula. Although the range of N. tarachodes extends westward to the Cape Peninsula, in these areas it is generally found at higher altitudes and further from the coast than N. dumeticola, and the two species evidently rarely co-occur. Has been observed feeding on the invasive snail Theba pisana (Müller, 1774) (W. Sirgel, in lit., vii/ 2012).
Conservation. Preservation of the delicate strandveld and sand fynbos habitats on the Atlantic Cape coast between Cape Point and St Helena Bay will be necessary for the conservation of this species. Much of the remaining natural habitat in this area is considered vulnerable or endangered (Mucina & Rutherford 2006). The West Coast National Park and the coastal parts of Table Mountain National Park have a significant role to play in this regard.
- 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: 24-27. doi