what class are sea urchins in
Sea urchins or urchins (/ËÉrtÊÉªnz/), archaically called sea hedgehogs, are small, spiny, globular animals that, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. About 950 species of echinoids inhabit all oceans from the intertidal to 5000 m deep.ea urchins feed mainly on algae, but can also feed on sea cucumbers and a wide range of invertebrates, such as mussels, polychaetes, sponges, brittle stars, and crinoids.