<p> Simple Marine Organisms – CORAL POLYPS & SEA ANEMONES</p><p>Similarities and Differences</p><p> Both coral polyps and sea anemones are cnidarians - soft-bodied organisms that sting their prey.  In both groups, individuals can reproduce sexually and asexually .  In many ways, sea anemones look like large versions of coral polyps .  An important difference between the two groups is that coral polyps are colonial organisms which form groups of thousands of individuals living in a common skeleton that we recognize as coral. When many of these groups form in a common area it is called a coral reef . </p><p> Due to the way they create their </p><p> calcium carbonate (CaCO3 ) skeletons, all coral polyps are sessile (cannot move) as adults.  In contrast, many sea anemones can move slowly along the seafloor using their muscular foot, or even detach themselves and swim awkwardly through the water.</p><p>Anatomy of Coral Polyps and Sea Anemones</p><p> Coral polyps are generally small , typically the size of a pencil eraser , but ranging up to about 2 inches in width.  Sea Anemones are generally much larger , ranging between 1 inch and 6 feet across!   They both have one body opening , stinging tentacles, a muscular column, and a structure to attach themselves to the substrate .</p><p>Feeding and Symbiosis in Coral Polyps and Sea Anemones</p><p> Coral polyps receive most of their nutrition from the sugar provided by the single-celled algae inside them called zooxanthellae .  Coral polyps also actively feed at night, emerging from the protection of their limestone skeleton to wave their tentacles in the currents to capture zooplankton and small fish .  In addition to capturing zooplankton and fish, many sea anemones also use single-celled algae to make sugars for them.  Some sea anemones have symbiotic relationships with hermit crabs, attaching to the shells of these crustaceans and providing protection to the crab while obtaining food from the scraps the messy-eating crab creates!  Of course, the more famous symbiosis with sea anemones involves the clownfish or anemonefish . Here the fish and a host-specific sea anemone provide mutual protection, while the wastes from the fish give nutrients to the sea anemone.  It is most likely that the mucous coating on the anemonefish prevents the sea anemone from stinging the fish. In addition, co-evolving with a specific sea anemone probably allowed the fish to acquire immunity to the venom of its sea anemone host.</p>