Description: Shell longer than wide (L / W ratio: 1.06 – 1.56; mean: 1.20), and moderately to strongly biconvex. Adult shells with pentagonal to subtriangular outline and widest in anterior portion of shell. Juvenile specimens with egg-shaped outline, though typically with weakly truncated front. Umbo short and stubby in adults, but somewhat narrow in juveniles. Anterior commissure changing from rectimarginate in juveniles, over broadly unisulcate, to distinctly parasulcate in adult specimens. Lateral commissure is straight to gently curved. Shell surface as a rule smooth except for sporadic growth lines, but large specimens can show sporadic radiating weak striation resembling that of Hemithiris. Shell white or straw-coloured. Shell matrix endopunctate. Circular, rather large and usually slightly transverse pedicle foramen developed in specimens over 6 mm long, but subtriangular to triangular deltidial plates disjunct in smaller specimens. Deltidial plates not separated from rest of shell by distinct beak ridges, but typically forms a raised ridge along midline when conjoined. Pedicle collar (thickening in pedicle tube) very short and lacking in juveniles. Ventral teeth never supported by dental plates. Hinge plates extended forward to join dorsal median septum in a V-shape. Brachial loop long and with wide transverse band. Brachial loop not attached to median septum on specimens longer than 13 mm. Long and low dorsal median septum reaches 60 – 84 % of valve length, except in juvenile specimens, and visible as a whitish knife-cut line on dorsal valve exterior. Juvenile specimens below 1.65 mm long lack dorsal median septum. A short septum with dot-shaped basis later evolves, which very soon becomes knife-cut shaped. Spicules in tissue mostly absent. Maximum shell length 45 mm. Depth range: 37 – 1800 m depth (Fischer & OEhlert 1892; this study), but common between 180 – 800 m. Temperature range: - 1.1 – 10.2 ˚ C (Carpenter et al. 1869; Jeffreys 1878). Salinity range: 34.9 – 36 (Thomsen 2001; Brand et al. 2003). Substrate: Attached to sand, gravel, corals, shells, bryozoans, serpulid tubes or Foraminifera (Atkins 1960 a; Thomsen 2001; this study). Sea bottom varies from silt- and sand-dominated to stony (Thomsen 2001).
Sumber: Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on