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The Echinoid Directory

Locomotion on the surface

Sea urchins move across the sea floor using their spines. Each spine is attached to the test by muscle and the spine bases are articulated via a ball and socket joint. Walking is effected by co-ordinated movement of the spines on the oral surface. Sea urchins can also climb up rock-faces and algal stipes using their tube-feet. Regular sea urchins have no preferred direction of locomotion and will lead with any of the five ambulacra. Irregular echinoids, on the other hand, always move forward with ambulacrum III leading.