My friend and I often see sand dollars on the beach. Usually they are broken. This morning, a broken sand dollar seemed to have a tiny starfish, about 15mm across, inside it.

I have discovered that a sand dollar is a type of starfish, or part of the species called echinoderm which has five-part symmetry, and what you can see inside this one is its eating mechanism. They are dead by the time they wash up on the beach – a bleached exoskeleton – which is why you often see fragments rather than the whole thing.