Opalescent nudibranch. This nudibranch feeds on hydroids, sea squirts, ascidians, other mollusks, various types of eggs and pieces of fish. Aeolids, including H. crassicornis, have many cerata (projections) along their bodies. The tips of these appendages are armed with stinging cells collected from prey animals like anemones. The centers of the cerata are used for digestion while the surfaces are used for respiration. This nudibranch is found from Alaska to Punta Eugenia, Mexico.