We’re all familiar with the common starfish (or maybe you call them seastars?) but did you know they’re part of a big family?
The Echinoderms have about 7,000 members worldwide and are named for the spiny skin which they all share – ‘echino’ means spiny. It’s not hard to guess that brittlestars are close relatives of starfish because like most of the animals in this group they have radial symmetry – if they were turned round there are several positions where they would look just like they did at the start.
Brittlestars have five legs, like many of the echinoderms (although some have more than 30). Instead of being seamlessly attached, the legs join a hard disc which forms the body. That bony central disc protects all their most important organs whereas the common starfish innards stretch down into their legs. This gives us a clue as to why they’re known as brittlestars – those legs can be sacrificed if they need to escape from a predator. They can cope with doing this as they can regrow them – but lost legs do not become new brittlestars.
Most echinoderms use their many tube feet to walk along but brittlestars don’t, they point a leg in their chosen direction and the others row them along – like a boat with two oars on each side. If they decide to change direction another leg takes the lead and the rest start rowing. Brittlestars can form beds across the sea floor, which helps them feed in strong currents. To stabilise the community they all link four of their arms and then hold the fifth aloft to collecting passing food particles – like fans waving lighters at a Take That gig!
We have many types of brittle star around the UK, some stay buried, but the two seen most often are the common brittlestar, which has stripy legs, and the black brittlestar which doesn’t, and oddly isn’t always black either!
For more information about SWT call 01473 890089 or visit www.suffolkwildlifetrust.org
The volunteer diving organisation Seasearch is run by the Marine Conservation Society and supported by The Wildlife Trusts. Visit www.seasearch.co.uk