This is a process where genes that are typically used during free-living periods aren't necessary because of the symbioses of the organisms. Without that gene, the organism is able to decrease the energy necessary for cell maintenance and replication. Among various types of symbiotic relationships, mutualism is where partners mutually benefit. Commensalism is a relationship where one partner receives a benefit while the other is not affected. There is parasitism, where one partner benefits while it is at the expense of the host. And amensalism is a less common type of relationship where one organisms receives no benefit but the host still has negative ramifications. The relationships can be an ectosymbiont, a symbiont that survives by being attached to the surface of the host which includes areas such as the inner surfaces of the gut cavity or even the ducts of endocrine glands. Or it can be an endosymbiont which is a symbiont that lives within its host and can be known as an intracellular symbiont. They are further classified by their dependence on their host and can be a facultative symbiont that can exist in a free living condition and is not dependent on its host. Or it can be an obligate symbiont which has adapted in such a way that it is not able to exit without the benefit it receives from its host. An example of an obligate symbioses is the relationship between microalgae and corals. The microalgae provides a large source of the coral diet  The most notable display of marine symbiotic relationship would be coral. Coral reefs are home to a variety of dinoflagellate symbiont, these symbionts give coral its bright coloring and are vital for the survival of the reef. The symbionts provide the coral with food in exchange for protection. If the waters warm or become too acidic, the symbionts are expelled, the coral bleaches and if conditions persist the coral will die. This in turn leads to the collapse of the entire reef ecosystem  "Osedax", also called the bone eating worm is a siboglinid worm from polychaete genus. It was discovered in a whalefall community on the surface of bones, in the axis of Monterey Canyon, California, in 2002. "Osedax" lacks a mouth, a functional gut and a trophosome. But female "osedax" have a vascularized root system originating from their ovisac which contains heterotrophic endosymbiotic bacterial community dominated by γ-proteobacteria clade.