Eleutherozoa

Sea urchin ( Prionocidaris hawaiiensis )

The Eleutherozoen are a subphylum of echinoderms. They comprise mainly motile, non- sessile species. Mouth and anus are located on opposite sides of the body, the mouth directed to the substrate. They are the Pelmatozoen ( Pelmatozoa ), consisting of the fixed crinoids and the free-moving hair stars, compared.

There are the following classes toward increasingly more derived forms:

• Starfish ( Asteroidea )
• Sea Daisies ( Concentricycloidea )
• Brittle stars ( Ophiuroidea )
• Sea urchins ( Echinoidea )
• Sea cucumbers ( Holothuroidea )