Feeding

Feeding in echinoderms covers a wide range of types and nearly every type of sustenance activity is represented by the

various species. Each type has body modifications that facilitate the way they obtain their food. Most sea stars are

carnivorous; eating clams, mussels, anemones, and even other sea stars. They have the ability to exude their stomach

through their mouth and digest their prey internally or swallow it whole and digest internally.

Sea Star eating clam. Photo from http://www.drizzle.com/~sunnym/other.htm

Some Brittle Stars and Crinoids are suspension feeders; sifting organic particles directly from the water

column and the tube feet of Crinoids have been modified to capture these particles. Other Brittle Stars are

detritus feeders, feeding on dead and decomposing organic matter. Sea Cucumbers and Sand Dollars are

known as deposit feeders; lying on the soft bottom, they scoop sediments into their mouth and sift out

whatever organic materials they can and then pass the unused portions out through the anus. Sea

Cucumbers have had some of their tube feet modified into tentacles to funnel the sediments into the mouth.

Sea Urchins are herbivorous, feeding on kelps and seaweeds. The Echinoids (Sea Urchins and Sand

Dollars) possess a special structure for feeding known as Aristotle's Lantern. It is a ring of calcareous

plates, similar to teeth that are connected to muscle tissue which extend and retract the structure, allowing

the animal to scrape off pieces of algae or scoop sediments.

Picture from Marine Biology by P. Castro.

Sea Stars and Brittle Stars have a relatively short, simple digestive tract while Sea Cucumbers and Urchins

have long, coiled tracts owing to their need for longer processing times of plant and sediment materials.

Once digested, the nutrients are transported by the coelomic fluid to the various tissues. Muscle action

within the body serves as the driving force for the fluid.