Swimming Anemone (Stomphia coccinea)

By Scott Boyd

The swimming anemone is one of the more photogenic of or our local invertebrates.  This beautiful, bright orange (with white stripes) anemone looks like a passive flower attached to the rocks along the bottom.  However, when approached by a predatory sea star (starfish), the “swimming anemone” lives up to its name by quickly detaching itself and swimming through the water using an undulating motion that is amazing to watch.  Sometimes, this swimming is less-than-elegant, and the anemone will tumble along the wall or bottom in a rather comical fashion as it escapes from the clutches of a deadly sea star.  (click on the photo for a larger version)

This beautiful anemone comes with remarkable offensive capabilities. Its tentacles are teeming with stinging cells, called nematocysts. These cells contain a hollow thread with a harpoon-like barb at the end. When the cell is stimulated by physical touch, it fires the barb and attached thread, simultaneously injecting venom. The amount of venom in each nematocyst is very small, but usually hundreds fire at once, which is enough to paralyze the anemone’s food.  This prey, which may include shrimp, crabs, jellyfish or small fish, is then moved to the mouth where it is consumed whole.

If you were to remove your glove, and touch an anemone’s tentacles, it would feel slightly “sticky” to touch.  This would be the nematocysts striking your fingers, and the threads creating that “sticky” feeling.  However, our fingers are pretty tough, and we don’t actually feel any effect from the toxin, as we are little too big to be prey.

The swimming anemone is easily identified by the distribution of its orange and translucent striped tentacles.  The inner ring of six tentacles usually stands vertical, and is surrounded by an outer ring of 10-12 tentacles that extend horizontally.