Sea urchin and anemone. Northern red anemone (Urticina felina, upper right) and pale sea urchin (Strongylocentrotus pallidus, lower left) on rocks. The northern red, or dahlia, anemone inhabits north Atlantic waters. It feeds on fish and crustaceans which are caught and stung by its tentacles. Sea urchins feed mainly on algae, but will also eat invertebrates such as mussels, sponges and brittle stars.