Sea Anemones

Sea anemone illustrations from Ernst Haeckel.
Ernst Haeckel, Kunstformen der Natur / Biodiversity Heritage Library

Sea anemones are members of the phylum Cnidaria, and as such are related to corals and jellyfish. Unlike jellyfish, however, anemones (and other anthozoans like corals) lack the free-swimming medusa stage. As sessile polyps, sea anemones have column-like bodies ending in an oral disk surrounded by tentacles that contain many stinging cells (cnidocytes) used for defense and capturing prey. The iconic clownfish are immune to these stinging cells’ toxin, however, and take refuge from their predators amidst sea anemones’ tentacles.