Tempuractis rinkai is a wild new genus and species of anemone which has a very peculiar relationship with a particular species of sponge. This tiny, simple anemone appears to be in an obligate symbiotic relationship with the sponge, living inside of them and retreating within for shelter.
There are many different types of symbiotic relationships in the natural world, and it is especially prevalent in the ocean where so many different kinds of creatures can interact. However, the description of Tempuractis rinkai represents what is believed to be the first obligatory association between an anemone and a sponge.
These little sponge anemones were discovered in shallow intertidal habitats in coastal Japan. The light orange colored sponge greatly resembles the tempura batter used to deep fry shrimp and vegetables in Japanese cuisine giving rise to one of the best genus names of all time, Tempuractis.
The reason for the symbiosis seems to be pretty straightforward, with the anemone gaining a place to shelter its unprotected body, while the stinging tentacles of the anemone dissuade sponge-eating nudibranch from grazing on its tempura style home. [BioOne]