Digestion

1. Digestion • Longitudinal grooves on the underside of each arm enable some species to locate food particles and transfer them by cilia to the mouth. • Other species wave their arms through the water column to capture plankton on sticky strands of mucus between arms.

2. Echinoidea • Echinos means hedgehog • Sea urchins and sand dollars • Globular with separate plates of calcite connected together. • Mouth on the underside and anus on upper side.

3. Sea Urchin Morphology • Mouth is on underside (ventral) and anus is dorsal (upper side). • Mouth has five sharp teeth connected to Aristotle’s lantern, made up of five separate jaws. • Mechanically grabs prey. • Lacks a stomach • Primitive nervous system • Note that the presence of a water-vascular system.

4. Inside an urchin

5. Digestion • Urchins can feed by taking bits of food into the mouth with complex grasping, chewing jaws or by absorbing food molecules into the mucus layer that covers their body and flows toward the mouth.

6. Holothuroidea • Sea cucumbers • Cucumber shaped body with leathery skin and spicules of calcite. • Have a ring of modified tube feet surrounding the mouth. • Live in muddy bottoms of bays and estuaries as well as continental shelves. • Eat mostly plankton but can extrude their stomach if they feel threatened. • Also can squeeze body into tight spaces by “liquefying” it temporarily.

7. Crinozoa • Sea lilies and feather stars • Usually have a base or holdfast to stay in place • A stalk is connected to a 5 plate disk at the top called a calyx which is used for filter feeding.

8. Morphology

9. Where they live • Live in clusters or “forests” ranging from warm, tropical water to icy polar waters. • Some are pelagic (feather stars) and prefer the clear waters of continental shelves. • Sea lilies are benthic and live on the deeper waters of the continental slope.