host by assisting with metabolism, nitrogen fixation, or cleaning the host organism. The diversity of advantages has yet to be fully explored, but by virtue of persisting throughout all of recent evolution, they likely confer an adaptive advantage to many of the species that exist solely due to ectosymbiosis. Types of Host and Parasite Dynamic Although, ectosymbiosis is typically an evolutionary stable behavior, the different host and parasite dynamics independently vary in their stability. Commensalism Commensalism is a form of symbiosis where one species is benefiting from the interactions between species and the other is neither helped nor harmed from the interaction. Ectosymbiotic commensalistic behavior is found frequently in organisms that attach themselves to larger species in order to move long distances or scavenge food easily; this is documented in remoras which attach to sharks to scavenge and travel. An additional ectosymbiotic example of commensalism is the relationship between small sessile organisms and echinoids in the Southern ocean, where the echinoids provide substrate for the small organisms to grow and the echinoids remain unaffected. Mutualism Mutualism is a form of ectosymbiosis where both the host and parasitic species benefit from the interaction. There are many examples of mutualistic ectosymbiosis that occur in nature. One such relationship is between Branchiobdellida and crayfish in which the Branchiobdellida acts as a bacterial gut cleaner for the crayfish species. Another example is the iron-oxide associated chemoautotrophic bacteria found crusted to the gills of Rimicaris exoculata shrimp that provide the shrimp with vital organic material for their survival while simultaneously supporting the bacteria with different organic material that the bacterial cannot produce itself. Groups of organisms, that is greater than a single pair of a host and parasite, can also form mutualistic ectosymbiotic interactions. Bark beetles can work in a dynamic mutualistic fashion with fungi and mites attached to their exoskeletons, both of which feed off of trees to provide vital energy to the beetles while the beetles provide necessary organic material to the fungi and mites to survive. In this case, the relationship between the fungi and mites is functional because while both do the same job, they are optimally functional at different temperatures. Mutualist interactions can be evolutionary unstable because of the constant battle to maximize one's self-benefits. This is due to the limited benefits offered to both the parasite and the host, with the possible outcome for at least one of the