The type of association exhibited by Hydroactinia and Pagurus is

Commensalism is defined as a type of a relationship between two organisms such that one organism receives a benefit from the other organism and the other is neither benefited nor harmed. Commensalism can be of two types. Ecto and endo commensalism. In ecto commensalism, the organism live in a commensal relationship on the exterior of another organism. Colonies of the hydroids, Hydracintinia echinata stay in the shells of Pagarus for shelter. The Pagarus, in turn, is unaffected. In endo commensalism, the organism resides inside the host.