Biology/Natural History: This species is usually solitary but occasionally a few clump together. This is the most common tunicate in the San Juan Islands but avoids areas of the highest currents. Its hemispherical body is often covered with sand, shell, or debris, and it has been called "the champion tunicate junk collector". The siphons project far from the body when feeding underwater, but can be retracted most of the way if disturbed or when out of the water. Diet includes crustacean, echinoderm, and mollusk larvae and eggs, as well as the larvae and eggs of tunicates. Predators include the seastar Solaster stimpsoni. May have the commensal copepod Pygodelphus aquilonaris or the protozoans Trichophyra salparum, Euplotaspis cionaecola, or Parahypocoma rhamphisokarya. May or may not brood its young (conflicting reports). Has gray eggs. The tunic is 13% organic, including 40% protein and 60% carbohydrate, but does not concentrate vanadium.
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