A sea urchin top (or 'aboral' to the initiated) view, found on Runswick Bay beach. Urchins are echinoderms, and exhibit pentamerism; five fold symmetry.
Its mouth parts.
And the mouth in which they were loosely attached when the shell was found. They fell out on handling. An urchin's mouth has the charming name 'Aristotle's lantern'.
urchin reproductive organs is a good idea and call it 'Uni'. Crabs, lobsters and sea otters are natural predators of urchins. Be careful if you find a live one, some species can sting.