Therasia thaisa Hutton, 1883

Pl. 4, fig. G

Hutton, 1883. The New Zealand Journal of Science, 1: 477.

Type material. Lectotype (designated here), CMNZ M12784 [ex M268], and paralectotypes (7), CMNZ M268 (dry shells). The molluscan collection at CMNZ has a shell, radula and jaw mounted on a glass slide with the label details ‘ Therasia thaisa, Southland, XVI p. 182’, in Hutton’s handwriting (i.e., CMNZ 2017.17.65–2017.17.66), which is probably primary type material (see descriptions of radula by Hutton 1884b: 182).

Label details. CMNZ M268—‘49. Therasia thaisa Hutton, Southland’, pillbox label in Hutton’s handwriting.

CMNZ molluscan catalogue details. M1045—‘ Therasia thaisa Hutton, Southland (old number ZS 690)’

Type locality. ‘Waiau, Southland (G. M. Thomson)’ (Hutton 1883g: 477, 1884b: 183).

Previous illustrations of type material. Jaw and radula teeth illustrated by Hutton (1884b: pl. 9, fig. M, pl. 11, fig. T) probably from type material; Pilsbry (1892 [in 1893–1895]: 346, pl. 3, figs. 14–16—‘ Type. Suter, del.’).

Remarks. Hutton submitted a description of this species to the Transactions and Proceedings of the New

Zealand Institute issue for 1883, but publication was delayed until May 1884 (Hutton 1884b: 182), and was preempted by a brief description in an account of a meeting of the Philosophical Institute of Canterbury (Hutton 1883g: 477). Therasia thaisa Hutton is the type species of Therasia Hutton, 1883, by subsequent designation of Pilsbry (1893 [in 1893–1895]: 15). Pilsbry had earlier (1892) nominated Nanina celinde Gray, 1850 as the type of Therasia, but this was invalid as the latter species was not in Hutton’s original list. There has been confusion over the identity and distribution of T. thaisa: it has variously been interpreted as having a wide distribution in New Zealand, from Auckland, in the North Island, to the southern South Island (e.g., Hutton 1884c: 202, Hedley & Suter 1893: 641, Suter 1894b: 247); or being present throughout the South Island and on Rakiura/Stewart Island, only (e.g., Suter 1913: 661, Powell 1979: 316). Preliminary results of a phylogenetic study, and examination of museum collections, indicate that the distribution of T. thaisa Hutton, 1883 is in fact restricted to the southern South Island, Rakiura and Whenua Hou/Codfish Island (M. Kennedy unpub. data).

Current taxonomy. Therasia thaisa Hutton, 1883 — Hutton (1884c: 202), Hedley & Suter, (1893: 641), Suter (1913: 660), Powell (1979: 316), Spencer et al. (2009: 216).

Distribution. New Zealand; southern South Island, Rakiura and nearshore islands, Whenua Hou (AIM and NMNZ collection records).