BIOL 1101 Lecture Notes - Lecture 90: The Sea Urchins, Brittle Star, Starfish
27 Jun 2016
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There are more fossil species (13,000) of echinoderms than there are living species (about 7,000). These organisms range from sea stars a half an inch or less in size to sea cucumbers larger than 6 feet in length. We will describe 5 of the classes of living echinoderms: Asteroidea ophiuroidea crinoidea echinodea holothuroidea sea starsbasket stars and brittle stars feather stars and sea lilies sea urchins and sand dollars sea cucumbers. They either eat dead animals on the bottom, or capture small invertebrates (snails, polychaetes, crustaceans, etc. ) and fish. Some sea stars employ a unique form of digestion. They are able to turn their stomachs inside-out and secrete digestive enzymes outside their bodies. These organisms can even slide their very thin and flexible stomachs between the shells of tightly clamped oysters and mussels, digesting the prey inside its own shell. Sea stars have been regarded as enemies by oystermen for centuries because of their destruction of oyster beds.
