Science, Tech, Math › Animals & Nature Understanding How to Classify a Sessile Organism What Coral and Mussels Have in Common Share Flipboard Email Print Andrea Cavallini / Getty Images Animals & Nature Marine Life Key Terms Marine Life Profiles Marine Habitat Profiles Sharks Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Forestry Dinosaurs Evolution View More By Jennifer Kennedy Marine Science Expert M.S., Resource Administration and Management, University of New Hampshire B.S., Natural Resources, Cornell University Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation. our editorial process Jennifer Kennedy Updated September 06, 2017 The term sessile refers to an organism that is anchored to a substrate and cannot move about freely. For example, a sessile alga that lives on a rock (its substrate). Another example is a barnacle that lives on the bottom of a ship. Mussels and coral polyps are also examples of sessile organisms. Coral is sessile by creating its own substrate to grow from. The blue mussel, on the other hand, attaches to a substrate like a dock or a rock via its byssal threads. Sessile Stages Some animals, like jellyfish, start their lives as sessile polyps in the early stages of development before becoming mobile, while sponges are mobile during their larval stage before they become sessile at maturity. Due to the fact that they don't move on their own, sessile organisms have low metabolic rates and can exist on small amounts of food. Sessile organisms are known to clump together which improves reproduction. Sessile Research Pharmacological researchers are looking into some of the potent chemicals that are produced by marine sessile invertebrates. One of the reasons for that the organisms produce the chemicals is to protect themselves from predators due to the fact that they are stationary. Another reason is they may use the chemicals is to prevent themselves against disease-causing organisms. The Great Barrier Reef The Great Barrier Reef was built by sessile organisms. The reef consists of over 2,900 individual reefs and covers an area of over 133,000 miles. It's the largest structure built by living organisms in the world!