4 Anemones

4 Anemones


4 Anemones

Painted Anemone

Urticina crassicornis


Friday Harbor Marine Laboratories, University of Washington

San Juan Island, Washington

Archival Pigment Print

A sea anemone is effectively a hollow sac filled with seawater, which enters and exits via a single opening—its mouth. When the animal is threatened, it contracts its muscles to quickly collapse and withdraw into itself, ejecting some or most of the water out of its mouth; even its hollow tentacles deflate. Re-emerging is a less hurried process: The anemone relaxes its muscles, and microscopic, hair-like processes (cilia) in the corners of its mouth get to work, driving water into the animal like tiny paddles. When fully inflated, the animal can seal its lips closed to prevent water loss.