Sea Urchin

Sea Urchin, Diadematidae (Samuel Chow / CC BY)

Sea urchins (class Echinoidea) are a group of echinoderms with globular or flattened bodies, that are typically covered with spines. The moveable spines of the Long-spined sea urchin (Diadema antillarum) are venomous and can reach up to 38 centimeters (15 inches) in length. On penetrating human skin, the spines easily break off. Fragments that remain in the wound may lead to bacterial infections. The venom causes a throbbing pain that can last for hours. Inattentive divers are at risk from contact with sea urchins during night dives or in shallow waters.

skull and crossbones
Some species venomous.

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This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.