The phylum Echinodermata includes a diverse group of marine animals that are slow moving and nonaggressive, including brittle stars (class Ophiuroidea), starfish (class Asteroidea), sea urchins (class Echinoidea), and sea cucumbers (class Holothuroidea). These animals have pentamerous (5-part) radial symmetry and calcareous skeletons that form thick outer plates and protective spines in some; hence, they are named Echinodermata, which means spiny skin. Injury and envenomation occur almost exclusively from accidental contact or careless handling; bathers, divers, and fishermen are at greatest risk.
Poisonous echinoderm ingestions or intoxications are not covered in this article. See the image below.
Echinoderm envenomations. Unlike most starfish that are typically pentamerous, the crown-of-thorns starfish (Acanthaster planci) may have as many as 23 arms and a body disc up to 60 cm in diameter. Photo courtesy of Dee Scarr.
See Deadly Sea Envenomations, a Critical Images slideshow, to help make an accurate diagnosis.