Echinoidea

Echinoidea is a class of marine animals that includes sea urchins and sand dollars. They have a hard, rounded shell called a test made of calcium carbonate, covered with spines that help them move and protect against predators. These creatures move slowly along the ocean floor using their tube feet and feed mainly on algae, scavenge, or filter particles from the water. Echinoidea play an important role in marine ecosystems by helping control algae growth and recycling nutrients. They have a five-part radial symmetry and are found in a variety of underwater habitats worldwide.