CREDIT NIAR / SCIENCE PHOTO LIBRARY CREDIT NIAR / SCIENCE PHOTO LIBRARY
Two nudibranchs (Chromodorididae) mating on a coral reef. Nudibranchs are hermaphrodites, having both male and female sex organs, but they cannot fertilise themselves. Nudibranch means naked gills , referring to the feathery structures (orange, upper left) through which they extract oxygen from the water.
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