Sea cucumbers are sausage shaped and have lost most of their skeleton. This enables them to squeeze and hide in small spaces. They have tube feet and a water pumping system to move them.
They move very slowly across the sea floor eating any decaying matter they find. They can be extremely common in some places.
The shape of their body means the mouth is at one end and the anus at the other.
Some species can protect themselves by pushing out of their anus a sticky mass of body organs. These grow back in a few weeks. The small pearl fish finds protection by entering the sea cucumber’s anus and hiding in the cloaca. Some segmented worms and crabs will also find protection inside the cloaca.