(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
[DOC] [TLE] Con Cu Gai , Sea Urchin, lp Cu Gai (Echinoidea) | Flickr [PAR] ... Sea urchins or urchins are small, spiny, globular animals which, with their ... 
Their shell, or "test", is round and spiny, typically from 3 to 10 centimetres ...