(Linnaeus, 1758)
Description
Body with a central disc of up to 35 mm in diameter and 5 short straight arms of about 3.5 times that length; colour varies from grey-brown to sandy-orange. The ventral side of the disc is of lighter colour.
Disc
The scales on the disc are rather coarse. The primary plates on the dorsal side of the disc are distinct, especially the central one. The radial shields are large, about 1/2 of disc radius. Arm combs consist of very fine papillae, ca. 30 in the outer comb (O. ophiura disc).
Arms
The dorsal arm plates in the notch above the arm (1) are rectangular or triangular. The free dorsal arm plates (2) in the proximal part of the arms are 4-5 times as broad as long, with straight or only slightly concave outer edge and completely contiguous (O. ophiura arm dorsal). The ventral arm plates are twice as broad as long, with a convex outer edge and they are separated by a pair of pore-shaped grooves in the mid-line of the arm. There are 3 pairs of arm spines lying flat against the arms. The tube foot pores in the proximal part of the arm have 3-4 tentacle scales, farther out 2 and distally only 1 (O. ophiura arm ventral).
Mouth
The mouth shields are large, occupying about 2/3 of the distance from disc edge to the adoral plate. There is a single, vertical row of teeth on top of the jaw and 4-6 mouth papillae on each side of the jaw (O. ophiura mouth).
Habitat
It is found on a variety of soft substrata, sometimes burrowing itself in sand or mud; from the low tide mark down to depths of at least 200 m.
Distribution
In the North Sea it is found on all coasts. Elsewhere it is distributed in the north-east Atlantic from Norway to Madeira, and in the Mediterranean.