Fotolia.com'>Sea urchins Echinoidea, or sea urchins, have radial symmetry, an external chitinous skeleton and a central jaw with teeth, known as Aristotle's lantern, according to Starfish.ch. The anus of sea urchins is located on the upper surface. Some sea urchins have a cloaca that extends out of the anus to excrete waste. Sea urchins move by using a tube foot that extends to pull the urchin along. Some urchins also use their spines to help with movement.