Crustaceans

Ancient animals – with armour!

Image taken by Paul Carter / paulcarter-photographer.co.uk Image © Sidmouth Museum
Image taken by Paul Carter / paulcarter-photographer.co.uk
Image © Sidmouth Museum

Crustaceans have been around for over 500 million years and many still look the same as they did back then. Most crustaceans live in the sea, including crabs, lobsters, shrimps and prawns, but the family also includes land creatures such as woodlice.

Crustaceans belong to the arthropods, a group of animals with an armoured external skeleton (called an exoskeleton), a segmented body and jointed legs. The hard exoskeleton is the part that’s preserved as a fossil. Arthropod comes from the Greek words ‘arthro’ meaning joint and ‘poda’ meaning foot or leg.


 

Coming out of their shells

Cast of an edible crab shell. If you find a 'dead' crab shell on the shore, pinch it between the eyes and if the top pops open, then it is actually a shed shell!
Cast of an edible crab shell. If you find a ‘dead’ crab shell on the shore, pinch it between the eyes and if the top pops open, then it is actually a shed shell!

Cast of an edible crab shell. If you find a ‘dead’ crab shell on the shore, pinch it between the eyes and if the top pops open, then it is actually a shed shell!Arthropods have a problem – they need to grow but are contained in a hard shell.  The solution is for them to shed their shells every so often. The shell simply pops open and the animal climbs out. Even the huge claws of a crab can be shed. But this leads to a second problem. The new shell is soft and flexible like latex, offering no protection from predators. So the animal has to hide away for a few days until the shell hardens. That is why ‘soft shelled crab’ makes such good fishing bait!

A tiny tell-tale

Tiny and potato-shaped, ostracods could appear to be one of our dullest crustaceans. But their fossils are of huge geological importance. Ostracods evolved very quickly through time. Therefore, like ammonites, individual species can be used to determine the age of the rocks they’re found in. Because they are so small (about 1mm), ostracods survive the drilling process in oil exploration. So they can be recovered and studied, helping provide clues to the location of oil reserves.