Nucula (Nucula) hawaiensis Pilsbry, 1921

Raines, Bret & Huber, Markus, 2012, 3217, Zootaxa 3217, pp. 1-106 : 8-10

Nucula (Nucula) hawaiensis Pilsbry, 1921

Figures 2 A–H

Nucula hawaiensis Pilsbry, 1921: p. 327 , fig. 11.

Nucula hawaiensis Pilsbry, 1921 — Dall et al., 1938: p. 7, pl. 7, figs. 4–7; Kay, 1979: p. 497, figs. 160 C–D; Severns, 2011: p. 428, pl. 195, fig. 2.

Nucula polynesica Rehder, 1980: p. 106 , pl. 13, figs. 1–2. (syn. nov.)

Nucula polynesica Rehder, 1980 — Tröndlé & Boutet, 2009: p. 4.

Material examined. More than 100 articulated specimens and single valves (2 to 3 mm) from EI and SyG (BK), plus specimens from the Hawaiian Islands ( MHU), and the holotype ( ANSP 116351 ) of Nucula hawaiensis .

Diagnosis. Shell small (up to 3 mm in length), solid and obliquely ovate. Strongly inequilateral with the umbones near the posterior end. Anterior margin long and evenly rounded, while the posterior margin is short, broadly rounded to somewhat subtruncate. Exterior surface smooth near the umbones which is gradually followed by fine commarginal growth striae, increasing in strength near the ventral margin. Interior nacreous, pallial sinus simple, ventral margin finely crenulated. Hinge line arched and consisting of chevron-shaped taxodont teeth, anterior with 6–10, and posterior with 4–5. Color white with brown periostracum on fresh specimens.

Remarks. Rehder (1980: 106) proposed a new species living in EI, from five worn valves collected in sand above the high tide level. He based his new species on three differentiating characters, namely a slightly larger size, a perceived lack of commarginal ridges, and number of hinge teeth.

After studying the holotype of Nucula hawaiensis Pilsbry, 1921 , and comparing specimens from both the Hawaiian Islands and EI, we came to the following conclusions: First, the size of 2.8 mm for the Hawaiian material, Kay (1979: 497), and 3.1 mm for the EI material, Rehder (1980: 106), is too close to be significant. Furthermore, none of the one hundred plus specimens collected by the senior author exceeded 3 mm.Second, not only the hinges but the dentition as well are very close. The Hawaiian specimens studied were within the range of Rehder’s species with 6–10 teeth. Kay (1979: 497) gave 10–11 teeth for adult Hawaiian specimens. Lastly, the decisive character, the lack of ventral ridges is non-existent. In well preserved EI specimens, these same ventral ridges are visible as in N. hawaiensis ( Fig. 2 B). Moreover, the shape is identical, the depth ranges are comparable and the general biogeography matches for 40% of all EI bivalves. Unless strong genetic signals were to separate them, we see little reason for two species.

Habitat. Commonly found around EI and SyG, in sand from 20–150 m.

Distribution. Currently Nucula hawaiensis is known from the Hawaiian Islands, Easter and Salas y Gómez Islands, as well as the Austral Islands— E4.