Sea cucumber anatomy, illustration. This marine animal is an echinoderm. Cylindrical in shape, it has five-fold symmetry with radii running from the anus to the mouth. Its mouth (and five feeding tentacles) is located at right. The intestine is long and coiled, looping through the body three times before terminating at the anus. Five major nerves run from the nerve ring at the mouth (yellow) down the length of the body. Sea cucumbers have no true brain.