Helix tau Pfeiffer, 1861

Brook, Fred J. & Ablett, Jonathan D., 2019, Type material of land snails (Mollusca: Gastropoda) described from New Zealand by taxonomists in Europe and North America between 1830 and 1934, and the history of research on the New Zealand land snail fauna from 1824 to 1917, Zootaxa 4697 (1), pp. 1-117 : 58-60

Helix tau Pfeiffer, 1861

Pl. 7, fig. B

Pfeiffer, 1861. Malakozoologische Blätter, 8: 148.

Type material: Formerly at least two syntypes in the Pommersches Landesmuseum, Stettin ( Murdoch 1899: 321– 322), but these were probably destroyed during World War II ( Dance 1966: 285, 1986: 222).

Type locality: ‘Neuseeland’ ( Pfeiffer 1861: 146).

Remarks: There are no published illustrations of the type material. The original description was based on specimens that were obtained by Ferdinand von Hochstetter during his visit to New Zealand in 1858–1859. There has been considerable confusion over the identity of this species (e.g., see Murdoch 1899: 321; and synoymies of Suter 1913b: 687, 714, 719; Powell 1979: 306; Climo 1969a: 201; Climo 1978a: 186). Pfeiffer’s original description of Helix tau did not mention the existence of apertural barriers, but a re-examination of two syntypes by Dr. Rudolf Sturany indicated that this species had “three deep inward running lamellae” within the aperture ( Murdoch 1899: 321–322). The most recent systematic revision by Climo (1978a: 186) listed Helix tau Pfeiffer, 1861 as a junior synonym of Helix infecta Reeve, 1852 , the type species of Fectola Iredale, 1915 , apparently on the mistaken assumption that the two species were based on the same type material (see Climo 1978a: 178). Climo (1978 a, 1989) recognised nine species of Fectola , two of which, H. infecta Pfeiffer and Fectola trilamellata Climo, 1978 , were characterised by having three strong apertural lamellae. Climo noted that H. infecta sometimes also had a weaker fourth lamella, whereas F. trilamellata did not, and had a smaller shell than infecta . Shells in the type series of Helix infecta have a flat-topped spire (e.g., pl. 5, fig. E), and a maximum diameter of c. 3.6 mm [3.7 mm for Helix zeta = H. infecta , according to Pfeiffer (1854a: 58)]. By contrast, Pfeiffer’s original description of Helix tau referred to a smaller shell (maximum diameter 3.0 mm), with a ‘slightly elevated spire, and minute crown’. The latter description and shell dimensions closely match Fectola trilamellata , and the two species are here considered to be conspecific, with tau Pfeiffer having priority. Given that the type material of Helix tau Pfeiffer, 1861 has most probably been destroyed, and in order to prevent ongoing confusion over the identity of this species and stabilise the nomenclature, we designate the holotype of Fectola trilamellata Climo, 1978 (NMNZ M.47455, Kaikoura, illustrated in pl. 7, fig. B), as the neotype of Helix tau Pfeiffer, 1861 , to ensure that synonymy is absolute and unequivocal.

Taxonomy: Fectola tau ( Pfeiffer, 1861) , n. comb. is accepted here as an available valid name. Fectola trilamellata Climo, 1978 is treated here as an objective junior synonym N. syn.

Distribution: New Zealand; central and southern North Island, and northeastern South Island (see Climo 1978a: fig. 4; Climo 1989: fig. 4—as Fectola trilamellata ).