(Sarah of the Clue Crew delivers the clue) Sea urchins' body symmetry makes their teeth fit together in a way that this pupil of Plato compared to a five-sided lantern.  2300 years later, it's still known as his lantern
Together with sea cucumbers (Holothuroidea), they make up the subphylum ... is 
known as Aristotle's lantern (image), from Aristotle's description in his History of 
Animals:.