Communication and Perception
Diadema antillarum has a highly developed light sensitivity. When a shadow appears, the urchin waves its spines in the direction of the shadow and moves away from the shadow, often into a more protected area. In this sense, D. antillarum can almost 'see' predators. It is not known how individuals communicate with each other to aggregate.
Communication Channels: chemical
Other Communication Modes: photic/bioluminescent
Perception Channels: visual ; tactile ; chemical