Musculus impressus ( Dall, 1907 )

Lisitsyna, Kseniya N. & Kamenev, Gennady M., 2024, New and rare bivalve species for the fauna of the Kuril Islands (northwestern Pacific Ocean): A study of materials collected over 70 years of expeditions (from 1949 to 2019), Zootaxa 5523 (2), pp. 231-253 : 240-241

Musculus impressus ( Dall, 1907)

( Fig. 3 E, F )

Modiolaria impressa Dall, 1907: 172 .

Musculus impressus ( Dall, 1907) — Scarlato 1981: 228, fig. 125.

Material examined: 91 specimens from the ocean and sea slopes of all the Kuril Islands and also from the Fourth Kuril , Krusenstern , Severgin , Rikord, and Snou Straits (1–500 m) .

Distribution: Kuril Islands, Bering Sea (1–500 m) ( Dall 1907; Scarlato 1981).

Remarks: Previously, this species was recorded only from waters off the northern Kuril Islands (two samples, three specimens) at depths of 100–130 m ( Scarlato 1981). Our data greatly expand both the geographical and the vertical ranges of this species.

Musculus impressus ( Dall, 1907) was synonymized with Musculus discors ( Linnaeus, 1767) ( Coan, Valentich-Scott & Bernard 2000) . However, after studying the description of Mytilus discors ( Linnaeus, 1767) and the photographs of a syntype of Modiolaria impressa Dall, 1907 (USNM 110467) from the USNM web site, we consider Musculus impressus ( Dall, 1907) to be a valid species.

Musculus impressus is clearly distinguished from M. discors by a much more elongate shell (the shell height to shell length ratio is almost 1:2) ( Scarlato 1981) with its posterior part highly raised relative to the middle part and a small number (6–8) of sparse radial ribs on the anterior part of the shell.

Figures

FIGURE 3. New and rare bivalve species for the fauna of the Kuril Islands. (A, B) Limatula attenuata (Iturup Island, 330 m, shell length 6.6 mm). (C, D) Limatula subauriculata (Iturup Island, 50 m, shell length 4.6 mm). (E, F) Musculus impressus (Urup Island, 123 m, shell length 17.7 mm). (G, H) Parvamussium intuscostatum (Onekotan Island, 146–147 m, shell length 17.2 mm). (I, J) Cardiomya cf. tosaensis (Urup Island, 100 m, shell length 7.8 mm). (K, L) Cetoconcha hyalina (Onekotan Island, 150–198 m, shell length 44.0 mm). (M, N) Dermatomya tenuiconcha (Simushir Island, 100 m, shell length 12.0 mm). (O, P) Poromya castanea (Iturup Island, 290 m, shell length 20.5 mm). (Q, R) Parvithracia sirenkoi (Paramushir Island, 400 m, shell length 7.0 mm). (S, T) Panomya ampla (Onekotan Island, 57 m, shell length 61.6 mm).