Decorator Crab
Decorator Crabs are very clever little crabs. They got so fed up with everyone trying to eat them, that they decided to do something about it.
These crabs discovered that they could actually grow sponges on their shell. They cut off little bits of sponge and stick them onto their legs and back. Being completely covered in sponge is more useful than it sounds - it makes them instantly toxic to eat and it is the perfect camouflage.
The only way you can spot one of these crabs underwater, is to wait for them to make a move. It's a bit of a give away when a sponge starts walking sideways.