Helix pilula Reeve, 1852

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 : 55-56

Helix pilula Reeve, 1852

Pl. 6, fig. B; Pl. 14, figs. E, F

Reeve, (1851–1854) 1852. Conchologia iconica, 7: species 809, pl. 132, fig. 809.

Type material: Syntype (1), NHMUK 20140673 (dry shell material); ex Museum Cuming (Acc. no. 1829). As noted by Cumber (1961: 179) and illustrated by Goulstone (2001: fig. 8A), this specimen has been badly damaged, with the base largely missing, and the upper surface of the last whorl broken.

Label details: ‘New Zealand’

Type locality: ‘New Zealand’ (Reeve 1852 [in 1851–1854]: species 809).

Previous illustrations of type material: Reeve (1852 [in 1851–1854]: pl. 132, fig. 809); Tryon (1886 [from Reeve 1852]: pl. 62, fig. 43); Suter (1897c: 284, text fig.); Goulstone (2001: fig. 8A).

Remarks: Helix pilula Reeve, 1852 and H. iota Pfeiffer, 1853 are based on the same type material; whether this originally comprised one or more specimens is not known. Pfeiffer evidently intended to publish the first description of this species in the Proceedings of the Zoological Society of London issue for 1851 (see Reeve 1852 [in 1851–1854]: species 809; Pfeiffer 1853a: 69), but publication was delayed until 1854 ( Pfeiffer 1854a: 57), and was pre-empted by Reeve (1852 [in 1851–1854]). There has been confusion over the identity of Helix pilula . Synoymies of Suter (1897c: 284, 285; 1913b: 666, 667) suggest that this species was in part misidentified as Phenacohelix granum (Pfeiffer) by Hedley & Suter (1893: 641), and that Flammulina (Phenacohelix) ponsonbyi Suter, 1897 was misidentified as pilula by Hutton (1884a: 161, 1884b: 194), Hedley & Suter (1893: 641) and Pilsbry (1893 [in 1893–1895]: 16). However, two of the locality records for pilula that were listed by Hutton (1884b: 194), namely Napier and Wellington, lie outside the distribution area of ponsonbyi (see Cumber 1961: 167, figs. 50, 58; Goulstone 2001: fig. 12), indicating that pilula of Hutton corresponded to ponsonbyi in part only. More importantly, Suter’s assertion that Pilsbry misidentified ponsonbyi as pilula does not stand scrutiny. The shell of pilula illustrated by Pilsbry (1893 [in 1893–1895]: 16, pl. 3, fig. 13) closely matches the ‘ type specimen’ of pilula illustrated by Suter (1897c) and is clearly not ponsonbyi . This has implications for the status of the genus Phenacohelix Suter, 1892 , which was listed by Suter (1892a: 270) as including Helix pilula Reeve , H. granum Pfeiffer , and H. chordata Pfeiffer , sensu Hutton (1884b: 194). Helix pilula was subsequently designated validly as the type species of Phenacohelix by Pilsbry (1892a: 56). However, Suter (1913b: 663) later incorrectly cited P. ponsonbyi as the type, based on his erroneous interpretation that pilula of previous authors corresponded to ponsonbyi . Ironically, Suter himself was somewhat confued as to the identity of ponsonbyi , with the type material comprising a mixture of two species, as noted by Cumber (1961: 164). More recently Bouchet et al. (2017: 185), following Suter (1913b), fixed Flammulina ponsonbyi Suter as the type species of Phenacohelix under ICZN Article 70.3 to “stabilize the application of the names Phenacohelix and Phenacohelicidae ”. In our view, this action is both unnecessary and inappropriate, as there is clear evidence that Pilsbry’s interpretation of pilula was not based on a misidentification, and we consider that the original selection of pilula as the type species of Phenacohelix should be retained.

There has also been confusion over the identity of Helix chordata Pfeiffer, 1861 . As mentioned above, the original description of this species noted that it “differs from the related H. iota Pfr. [= Helix pilula Reeve, 1852 ] in the top-shaped [turbiniform] spire and the almost closed perforation”. Early New Zealand workers recognised pilula and chordata as separate species (e.g., Hutton 1880: 5; Suter 1892a: 270; Hedley & Suter 1893: 642; Suter 1913b: 664), but Cumber (1961), and Powell (1979), listed chordata as a junior synonym of pilula . The two last-mentioned authors also listed Flammulina (Phenacohelix) leptalea Suter, 1907 , as a junior synonym of pilula . Conversely, Goulstone (2001) described two new species from material that had previously been identified as pilula , namely Phenacohelix aurea and P. mahlfeldae . Phenacohelix pilula , as interpreted following Goultone (2001), has a wide geographic distribution in New Zealand (below), and shows considerable variation in umbilical width, spire elevation, and rib-spacing, both within and between populations (see also Cumber 1961). Further work is required to determine if this is a single species or a species complex.

Current Taxonomy: Listed as Phenacohelix pilula (Reeve, 1852) by Suter (1892a: 270, 1913b: 666), Hedley & Suter (1893: 641), Cumber (1961: 177), Powell (1979: 322), Goulstone (2001: 66) and Spencer et al. (2009).

Distribution: New Zealand; North Island, and northern & eastern South Island ( Goulstone 2001).