Echinoderms Phylum Echinodermata Echinos means hedgehog derma means

Echinoderms

Phylum Echinodermata • Echinos means hedgehog, derma means skin • Includes: Sea stars, sea urchins, sea cucumbers, brittle stars, sand dollars, sea lillies • 6, 000 marine species • Radial symmetry based on five sections or projections. • Defined by a water-vascular system

5 Classes • Asteroidea • Sea Stars • Ophiuroidea • Brittle Stars • Echinoidea • Sea urchins and sand dollars • Holothuroidea • Sea Cucumbers • Crinozoa • Sea lillies and feather stars

Where they live • Intertidal and subtidal zones from the continental shelf to the continental slope. • Some are infaunal and some are epifaunal

Asteroidea • Aster means star, oidea means resembling • Sea stars all of which have between five and 25 arms around a central disc. • Arms have spiny projections on top and delicate tube feet beneath • Tube feet work like suction cups and can grip objects and participate in gas exchange.

Water-Vascular System • Sea stars and all echinoderms have a water-vascular system to help them with movement and feeding • System is a complex of water-filled canals, valves, and projections. • Operates like a hydraulic power system • Can transmit forces generated by muscles at one side of the sea star to arms on the other side. • Using this, the sea star can grip to a clam or mussel and exert continuous pull for hours to open the valves.

Water-Vascular System

Digestion • Sea stars expel their stomach from their mouth and digests the opened mollusk in place.

Sea Star/Starfish Morphology

Ophiuroidea • Ophidion means snake. • Brittle stars and basket stars • Called brittle stars because if they are caught by a predator, they will detach the arm and escape. • Later, it can regenerate the missing arm. • Most widely distributed benthic marine organism. Many live on sediment on ocean floor or beneath intertidal and subtidal rocks.