Ophiactis balli

(Thompson, 1840)

Small Banded Brittle Star

Body with a central disc of up to 5 mm in diameter, with 5 arms of about 6 times that length. Colour of disc reddish, the arms are usually banded with red-brown and whitish.

The dorsal side of disc covered with small scales, on the oral side even finer scales. Generally, there are no spines on the dorsal side, only on the edge and the ventral side. The primary plates are not distinct. The radial shields are small and separated by a wedge of scales (O. balli disc).

The dorsal arm plates are triangular, the ventral ones rounded. In the proximal part of the arm there are 5 (elsewhere 4) rather short, conical arm spines per segment. Tube foot pores largely covered by 1 fairly broad tentacle scale (O. balli arms).

Mouth shields are rounded triangular. There is a single infradental papilla on top of the jaw and one small mouth papilla on each side of the jaw, not contiguous with the infradental papilla. Two pairs of tube-feet within the mouth (O. balli mouth).

This species is found on hard substrata where it conceals itself in small cavities in stones, shells etc. It occurs mainly in depths of ca. 60-400 m, but has been found down to 1765 m.

In the North Sea this species has been found as far south as Northumberland and Durham on the east side and the Scandinavian coasts on the west side. It is distributed from the Scandinavian coasts in the North, to the Canary Isles in the South. It is not known from Greenland or the American coast.

Ophiopholis aculeata is known from similar habitats and has a similar colouration, but is larger and coarser.