Echinoderms (phylum Echinodermata) are one of the best-known
groups of marine invertebrates. Sea urchins and starfish, despite their
apparent differences, are part of the same group and share characteristics
such as five-radial symmetry. This phylum has an aquatic vascular system with
many ambulacral grooves with tube feet, which it uses for locomotion,
capturing prey, and breathing. In addition, it has an internal skeleton
made of calcareous plates. These creatures lack a brain or eyes,
so they use photoreceptors to sense movement.