Commensalism is the relationship between individuals of two species of which one is benefited while the other is neither benefited nor harmed. The organism that derives benefit is called the commensal. The association may be temporary or permanent.
Sucker fish and Shark: Sucker fish (Echeneis) get attaches to the underside of a shark by means of its sucker (modified dorsal fin).
The sucker fish is taken to distant areas with better food supply. The fish also gets protection from predators due to its association with shark. The shark does not any benefit from sucker fish and it is also not affected adversely.
Polyonx and Chaetopterus: The crustacean Polyonx lives inside the ‘U’ shaped tube of Chaetopterus (marine polychaete). Polyonx gets protected shelter food and oxygen. Chaetopterus is not harmed.
Epiphytes: Some plants like mosses, ferns, orchids, money plants etc. grow on large plants utilizing only space for attachment. These epiphytes get better light conditions and do not harm the tree.