Sea Urchin

© Jean Tresfon


Sea Urchin (Echinoidea)


Sea urchins measure 12 cm on average but can be as big as 36 cm.

Sea Urchin Identification

Sea urchins are covered in spines of different thicknesses and lengths and have round bodies and a calcium carbonate shell. They vary in colour from black to blue, green, white, red and orange.

Sea Urchin General Info

Sea urchins are a part of the Echinoidea class which falls under the Echinodermata phylum, which includes sea cucumbers and all the stars – sea, feather and brittle.
They have tiny tubular adhesive feet on which they move, and can be found on reefs or covered in sand. Their bodies are radially symmetrical, similar to the spokes of a wheel. Stepping in their spines can cause an agonising wound, and possibly an infection if the spines break off.

Sea Urchin Feeding

Sea urchins are grazers, feeding on algae and detritus.


They can be found in all temperate and tropical oceans across the world.

Common Species

Flower urchin
Toxopneustes pileolus
Needle urchin
Diadema setosum
Slate pencil urchin
Heterocentrotus mammillatus