Volutopsius gracilis Mclean & Clark 2023, n. sp.

Volutopsius gracilis n. sp.

Figure 19 D–E urn:lsid:zoobank.org:act: 58A8BD6B-DF20-4AF2-BCB9-5296AA4DEF48

Type locality: E of Shumagin Islands, Aleutian Ids., Alaska (55°42.75 N, 158°52.65W); 97 m. (NMFS 143-2015 - 1-62).

Type material: Holotype: LACM 3589; Paratypes: Pt 1, LACM 3604, 142.1 mm. N of Unimak Island (56°41.06 N, 165°51 W), 80 m (ex - Rae Baxter, LACM 1984-106 105.5 mm); Pt 2, SBMNH 169016, 103 mm. Wide Bay, S side of Alaska Peninsula (57°11.13 N, 156°07.03 W), 91 m (NMFS 147-200301 - 125); Pt 3, RNC 5031, 86.5 mm. W of Trinity Islands SW of Kodiak Island (56°41.56 N, 152°54.96 W), 71 m (94-200901-183).

Referred material: RNC 4505, 90.2 mm. Unimak Pass, N of Akun Island (54°21.19 N, 165°35.51 W), 146 m (94-199401-9); RNC 4858, 108 mm. W of Trinity Islands SW of Kodiak Island (56°41.56 N, 152°54.96 W), 71 m (94-200901-183).

Description: Shell large for genus (to 142 mm; LACM 84–106.5), elongated; whorls sub-angulate; cream to light brown, with very thin tan periostracum. Protoconch smooth, with 1.5 whorls; teleconch with 3.5 whorls; axial sculpture variable, smooth or irregularly wrinkled; spiral sculpture usually lacking, but may have 5–8 faint spiral cords at mid-whorl. Aperture slightly more than half of shell height; canal short, narrow. Operculum less than half of aperture height, nucleus terminal.

Radula: Typical for genus, lateral teeth with two large, curved cusps; rachidian tooth with seven cusps, outer cusps much larger than, inner ones, five inner cusps small, slender, of unequal length, equally spaced.

Remarks: Kantor (1990) reviewed the Volutopsiinae, and concluded that Volutopsius stefanssoni Dall, 1919 (figs H–J) (along with what appears to be V. gracilis) was synonymous with Volutopsius castaneus (Mörch, 1857) (figs. 19 F–G), however Kessler (1985) had previously demonstrated that the two were distinct. Kantor also considered Volutopsius simplex Dall, 1907 (fig 19 J) to be a variety of V. castaneus, but morphologically it appears to be a smooth, round-shouldered form of V. stefanssoni. Volutopsius gracilis is very similar to V. castaneus with which it has long been confused, but from which it differs in 1) larger size 140+ mm compared with 100 mm for V. castaneus; 2) shell proportions, slender profile, aperture a little over ½ of shell height, compared with compact profile, aperture about 2/3–3/4 of shell height in V. castaneus; 3) Rachidian tooth with seven cusps, opposed to five in V. castaneus; 4) Geographic distribution, V. gracilis is restricted to the vicinity of the Alaska Peninsula, whereas V. castaneus has a much broader range, from Adak Island (177°W) east to the Kenai Peninsula (148°W). Although the type of V. castaneus was said to have come from Sitka, Alaska, no specimens have been verified from the eastern Gulf of Alaska (Clark, 2018). It more likely came from the vicinity Kodiak Island, or perhaps Unalaska Island. The range of V. castaneus appears to extend around the Bering Sea shelf to Kamchatka. 5) Bathymetric distribution, V. castaneus is a shallow, in shore species, commonly found at 1–35 m, and rarely below 50 m, whereas V. gracilis is an off-shore species, found below 70 m, and 6) Shell color V. gracilis is always cream to light brown, whereas V. castaneus may be orange-brown dark brown, tan or white.

Volutopsius gracilis forms a complex with similar (often axially sculptured) species (Clark, 2018): Volutopsius castaneus (Mörch, 1857), Volutopsius stefanssoni Dall, 1919, Volutopsius trophonius Dall, 1902.

Etymology: The name is from the Latin, for slender.

Distribution: Alaska Peninsula, vicinity of Unimak Pass (165°W), from north of Unimak Island, south and east to south of Kodiak Island (152°W), at depths 71– 146 m.

Habitat: Mud, muddy-sand and gravel bottoms, at bottom temperatures of 4.6°–6.3°C.