Ophiura ophiura

Ophiura ophiura, called the serpent star, is a brittle star belonging to the order Ophiurida. It lives on coastal seafloors near northwestern Europe.

Description

Its body has a round central disc up to 35 mm wide, with five narrow arms arranged around it, each reaching up to 140 mm long. The animal is mottled reddish-brown on top and paler underneath. Both the upper and lower surfaces of the disc are covered with calcareous plates.

The arms attach to the top of the disc, not the edge, and small articulating plates let them bend sideways. Tiny spines on the arms lie flat. At the base of each arm are four larger plates; the outer pair have comb-like edges with 20 to 30 fine papillae each.

A pair of pores sits between the underside plates at the arm roots. On the disc’s underside, five large mouth-shield plates surround the central mouth. Each of the five jaws has a vertical row of teeth above it, and about five mouth papillae line each side of the jaw.

Distribution and habitat

This brittle star is found on the seafloor in the northeast Atlantic Ocean and the North Sea, from Norway and Sweden south to Madeira and the Mediterranean Sea. It occurs below the low-tide mark in the neritic zone down to about 200 m, on sandy bottoms. It prefers fine-grained sediment with about 35% mud content. It is common, with 20 to 50 individuals per square meter in some years in the North Sea.

Biology

Ophiura ophiura is active, moving with a jerky swimming motion of its legs and sometimes burrowing. It filter-feeds on a wide range of food, but also acts as a bottom-feeding carnivore and detritivore.

It can regrow arms that are damaged or torn off. Sexual reproduction happens in summer. The larvae are typical ophiopluteus larvae, which later settle on the seabed and develop into juveniles.

Ecology

The copepod Parartotrogus richardi is an ectoparasite of O. ophiura. In the Clyde sea fishery for scampi (Nephrops norvegicus) in Scotland, unwanted invertebrates caught in trawls include O. ophiura and the starfish Asterias rubens.

A study on survival rates after discarding found that uninjured A. rubens had a 4% mortality rate, while nearly all O. ophiura died within 14 days, even if returned to the water immediately. Another study looked at how fast discarded invertebrates sank and what happened to them. O. ophiura sank slowly, was eaten by seabirds, and its arms were consumed by fish.