Ophiomusium planum Lyman, 1878 — $ Koehler 1896b: 242, 1906b: 265–266, 1909: 162, pl. 29, figs. 11; Mortensen 1927a: 252; Grieg 1932: 36; Nobre 1938: 145; García-Diez et al. 2005: 49;
Ophiomusium armigerum Lyman, 1878 — $ A.H. Clark 1948: 78; $ Cherbonnier & Sibuet 1972: 416.
Type locality: between Tristan da Cunha and South American continent (37°29’S, 27°31’W).
See: Lyman (1878: 108, 109–110, pl. 1, figs. 21–22, as Ophiomusium armigerum); Paterson (1985: 149, fig. 58).
Occurrence: Atlantic, East coast of United States from off Virginia to the Caribbean Sea (Koehler 1914a) and Gulf of Mexico (Lyman 1883), south to off South America (Lyman 1882), in the East Atlantic known from the Bay of Biscay (Cherbonnier & Sibuet 1972) to NW Africa (Koehler 1906b), including the Azores (Koehler 1909), Madeira (Lyman 1882) and Canaries (Paterson 1985).
Depth: 260– 5,110 m (Lyman in Koehler 1914 a, Cherbonnier & Sibuet 1972), mainly found from 3,000 –5,000 m (Paterson 1985); AZO: 2,870 –5,005 m (Koehler 1909, Cherbonnier & Sibuet 1972).
Habitat: soft sediments, clay, mud to ooze (Lyman 1882, Koehler 1909).
Remarks: Ophiomusium planum was reported from the Azores by Koehler (1896b, 1906b, 1909) and Cherbonnier & Sibuet (1972), based on material collected by Princesse Alice, Talisman and Noratlante. A.H. Clark (1948) reported Ophiomusium armigerum collected by Atlantis in the archipelago. Later, Paterson (1985) found these species to be conspecific and established the synonymy.