This type of mutualisn to called protocooperation. In this type, the sea anemone grows on the back of the hermit crab. It protects the crab with the help of its nematocysts. Ectoparasites live on the outside of host, e.g., human body louse. In this interaction, the parasite gets the benefit at the expense of the host. Commensalism is an assotiation between organisms in which one or both the species are benefitted and neither species is harmed. In amensalism one species is harmed, whereas the other is unaffected. Predation, parasitism and commensalism share a common characteristic, the interacting species live closely together.