How are the symmetry and the nervous system characterized in echinoderms?
Adult echinoderms, along with cnidarians, are the animals that present radial symmetry, i.e., their body structures are distributed around a center. The radial symmetry in echinoderms however is a secondary radial symmetry, since their larval stage has bilateral symmetry and the radial pattern appears only in adult individuals (there are some few adult echinoderms with lateral symmetry). All other animals have lateral symmetry with exception of poriferans (no symmetry is defined for them). Echinoderms do not present cephalization and they have a diffuse network of nerves and neurons made of a neural ring around the mouth and of radial nerves that ramify to follow the pentaradial structure of the body.
