What characteristics do sea starssea urchins and brittle stars have in common?

Sea stars, sea urchins, and brittle stars all belong to the phylum Echinodermata, which is characterized by their radial symmetry, a water vascular system, and a calcareous endoskeleton made up of ossicles. These marine animals also exhibit regeneration capabilities, allowing them to regrow lost limbs or parts. Additionally, they all possess tube feet, which aid in locomotion and feeding, and they are primarily found in ocean habitats, often on the seafloor.