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Sea Stars

Metridium Anemones


Anemones are part of the Phylum Cnidaria, along with jellyfish and corals.  Cnidarians have two body forms, one free-swimming, called a medusa, and the other is stationary and called a polyp.  Jellyfish have the medusoid body form, with a bell-shaped body and tentacles along the edge of the bell. A polyp such as a sea anemone is essentially a jellyfish turned on its head, with its body more tube-shaped and the tentacles directed upwards into the water column

 Most sea anemones are predaceous, immobilizing their prey with the aid of specialized stinging cells called nematocysts.  Metridium Giganteum is the species that we are most familiar with as Pacific Northwest Divers.  This large, fluffy white anemone is found throughout the region attached to docks, pilings and other hard substrate.  It can also be found in colors ranging from orange to a brown or tan color.

Like other animals in the phylum Cnidaria, plumose anemones feed on small plankton (drifting animals and plants), that they capture with their stinging cells. They, in turn, are eaten by several different kinds of animals, including the nudibranch, Aeolidia papillosa, and the Leather star (Dermasterias imbricata.)

 Metridium Anemones have been observed reproducing by “cloning”, where the animal actually splits in two to form two identical Polyps.  Individual animals can live to be several centuries old, and have lived nearly 100 years in aquariums before dying due to equipment malfunction ( not old age ).  Scientific studies have shown that the size of an adult Anemone is closely related to the speed of the current.  They feed most efficiently from the eddies created by the current flowing over the back of their head, with larger animals more predominate in moderate currents.