The symbiotic relationships of organisms has the ability to change behavior, morphology and metabolic pathways. Other microbes in deep-sea vents have been found to prevent the settlement of barnacles and tunicate larvae. Various mechanisms are utilized in order to facilitate symbiotic relationships and to help these associates evolve alongside one another. By using horizontal gene transfer, certain genetic elements are able to pass from one organisms to another. In non-mating species, this helps with genetic differentiation and adaptive evolution. An example of this is the sponge Astroglia Willena which has a gene that is used in expressing spherulite-forming cells which has an origin in bacteria. 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 mentalism is a less common type of relationship where one organism receives no benefit but the host still has negative ramifications. 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.