Nausithoe sp., Nausithoidae, coronate jellyfish, polyps, cnidarians, jellyfishes, unidentified sponge, marine invertebrates, sponges (porifera), behavior, interspecific relationships, symbiosis, mutualism, inquilinism, underwater, El Hierro Island, Canary Islands, Spain, Atlantic Ocean.

Remarks: Some jellyfish have a polyp shape during the larval stage. In this case the polyps live inside a sponge. Research has proven polyps protect the sponge against predators. Therefore, both especies obtain benefit (mutualism). The polyp finds a refuge inside the sponge (inquilinism) and the sponge avoids being devoured. In addition, the sponge uses the external structure of the polyp as if it was an internal skeleton.