Echinoids are one of the more diverse and successful echinoderm groups today, including familiar echinoderms such as the sea urchins and sand dollars.
Sea urchins or urchins, also known as sea hedgehogs, are small, spiny, animals that constitute the class Echinoidea of the echinoderm phylum. Sea urchins eat plant and animal matter, including kelp, decaying matter, algae, dead fish, sponges, mussels, and barnacles. Sea urchins are 12 ft long and weigh about 3 lbs. Red sea urchin has the longest lifespan on Earth. It can survive up to 200 years in the wild.