The number of arms ranges from 5-20, and all are carnivores. Class Echinoidea includes sea urchins and sand dollars. These animals lack arms and have their endoskeleton plates fused into a solid shell. Sea urchins have long spines that are used for such functions as protection. Sea urchins are herbivores.
Sand dollars eat organic material found in sand.
Class Ophiuroidea includes the brittle stars. These animals have long, slender arms that break off easily. The arms are used for swimming. Brittle stars are carnivores. Class Holothuroidea includes sea cucumbers.