Figures 42 a, b, c
Ophiomusium armigerum Lyman, 1878; H. L. Clark, 1915.
Ophiomusium planum Lyman 1878; Madsen, 1951; Vadon & Guille, 1984; Paterson, 1985. Ophiosphalma armigerum (Lyman 1878); H. L. Clark, 1941; Paterson, 1985.
Snytype BMNH 82.12. 23.177, Challenge r station 332; syntypes, MCZ 451 (2) off Japan 3429m; MCZ 441 (4) Challenge r station 106, mid-Atlantic, 3383m; MCZ 475, Blake Expedition, Gulf of Mexico, 1820m (holotype of Ophiomusium planum Lyman).
Main features: Many small disc scales with protuberant primaries visible. In largest specimens (<17 mm d.d.) the primary disc plates are a different texture to other scales—they are similar to the radial shields and therefore stand out. Radial shields and interradial areas separated by many small oval scales. Radial shields large. Genital slits slightly longer than the first arm segment, with bordering papillae. Oral papillae block-like, not pointed, and not separated. Oral shield varies from oval to lemon-shaped. Dorsal and ventral arm plates large and throughout the arms. Three, occasionally 4 pairs of exposed tentacle pores, with 2 or 3 scales on the first pores. 6 - 3 very small arm spines.
This species is similar to O. elegans Koehler, except that the shape of the oral shield differs, and oral papillae are not separated and free, as in elegans. Ophiomusium planum Lyman was synonymised with O. armigerum by Paterson (1985), and I concur with that decision.
A syntype of Ophiosphalma armigerum var congense (Hertz, 1927) from Valdivia Station 63 (ZMUC) is 20 mm d.d., and differs from armigerum only in the dorsal surface of the disc being covered with many small scales, closely soldered, with scattered larger circular granular scales, which look similar to moon craters. There are 3–4 short arm spines, the 2 nd to lowest being the longest. Until more material becomes available, congoense should remain asubspecies of O. armigerum. (Note: this specimen in the ZMUC was mislabelled O. fimbriatum var atlanticum).