Crinoids are delicate and graceful marine animals – they’re also called sea lilies because they look like underwater plants.
They belong to the same family as sea urchins and starfish.
Crinoids don’t move much – they attach themselves to the sea bed or floating drift wood using tiny hooks called cirri. But if they’re threatened by a predator some can let go and swim by undulating their arms.
Crinoids feed on tiny plankton which they catch with their sticky arms.
Crinoids have been around for almost 500 million years and still exist today, usually in tropical waters.
Sometimes many crinoids are packed into one rock. This is because they lived on driftwood and when that sank, the whole colony became fossilised together.