They are invertebrates, under the phylum Echinodermata,
consisting of five fragile arms with small thorns that are used to help move along the seafloor and can regenerate if broken off. Connecting the arms is a disk which contains all of the internal organs. The disk can be up to 1.8 - 2.5 cm. The mouth is found on the under side of the disk and is rimmed with five jaws, which serves as both mouth and anus. They reproduce by broadcast spawning.
They don't have eyes or specialized sense organs. Instead, they have sensitive nerve endings on the ends of their arms that can sense light and odor. Being without a brain, they have a ring of nerve cells around the disk that sends information throughout their body. These creatures are detritivores and eat decaying matter, plankton, small suspended particles, and they also prey on small crustaceans and worms.