THE BRITTLESTAR FILE
This creature is all arms, and it can do a lot of things with them, says Paul Naylor
Brittlestars are also known as serpent stars. The snake-like movements of their individual arms propel them surprisingly rapidly across the seabed. Tube feet don4t walk them along as in starfish, but merely act like running spikes to give the highly mobile arms some grip.
Brittlestars can devour tiny animals whole, but they are generally scavengers, browsers and filter-feeders. Some will hold themselves in position with two arms and raise the others up into the current so food particles are trapped by the tube feet.
GALAXY OF STARS
Enormous aggregations of the common brittlestar (pictured) can contain up to 10,000 individuals per sq m. Black brittlestars retain relatively more of their own space when grouped. Many other species lead far less obtrusive lives, hidden in crevices or buried in sand with only their arm tips exposed.
In rough weather or strong tides, the brittlestars that are gregarious help each other out by linking arms. Individuals separated from their neighbours get swept off by the current, while the main patch manages to stay put.
ARMS TO SPARE
Living up to their name, brittlestars have extremely fragile arms. Some will sever them deliberately as an escape mechanism if seized by a predator, and will then re-grow them later. Predators of brittlestars include their starfish cousins and fish such as haddock and dab.
REASONS TO BE SLIM
Brittlestars might look just like their starfish relatives on an extreme diet, but there are other major differences too. For example, brittlestars have a much simpler gut system with no exit, so undigested material is discarded through the mouth.