Two bright orange anemonefish (Amphiprion ocellaris) poke their heads between anemone tentacles. Anemonefish are able to swim amongst the stinging tentacles without getting stung — but no one knows exactly sure how. One dominant theory explains that they have a protective slime coating their bodies. However, anemonefish are not born with this protective slime and scientists don't know how they develop it.
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Clownfish in their Host Anemone

Flickr user Jenny Huang (JennyHuang)/EOL