Pascahinnites pasca ( Dall, 1908 )

Raines, Bret & Huber, Markus, 2012, 3217, Zootaxa 3217, pp. 1-106 : 36-37

Pascahinnites pasca ( Dall, 1908)

Figures 17 A–H

Pecten (Chalmys) [sic] pasca Dall, 1908: p. 401 .

Chlamys pasca ( Dall, 1908) — Rehder, 1980: p. 109, pl. 13, figs. 3–6.

Pascahinnites pasca ( Dall, 1908) — Dijkstra & Raines, 1999: p. 200, figs. 1–2; Raines & Poppe, 2006: p. 222, pl. 170, figs 1–4; Tröndlé & Boutet, 2009: p. 6; Dijkstra & Maestrati, 2010: p. 339 , figs. 3 L–M.

Material examined. Over one hundred articulated specimens and single valves (3.2 to 19.6 mm) (BK).

Diagnosis. Chlamydoid shell, small (up to 20 mm in height), slightly equivalve and equilateral; umbonal angle ca. 90–95 o. Left valve with 12–14 prominent primary radial ribs, and numerous intercalated secondary ribs toward the ventral margin. Shagreen microsculpture throughout except on crest of ribs, where fine spines may be present. Radial ribs of RV bi- or tripartite, and weaker and less angulated than those of the LV. Auricles unequal in size (anterior larger than posterior), with small prickly radial riblets, more prominent on anterior auricle. In juveniles and subadults, byssal notch moderately deep, with active well developed ctenolium consisting of 4–6 teeth. Valves of mature specimens distort after 9–11 mm, due to changes in preferred habitat. Color variable, whitish, creamy, yellowish or rose-pink with spots and/or streaks; RV paler than LV.

Remarks. Adults up to about 10 mm are either free swimming or byssally attached. Once mature they appear to prefer colder water and live cemented to hard substratum. This change in habitat tends to strongly distort the valves in order to accommodate the surface of the selected substrate.

Habitat. Commonly found at many locations around EI and SyG, from 10–150 m. Free swimming or byssally attached as juveniles in shallow water (10–30 m), while adults are cemented to substratum below 50 m.

Distribution. Pascahinnites pasca was previously thought to be endemic to EI and SyG, but it has been recently recorded from the Austral Islands as well, Dijkstra and Maestrati (2010) — E4.