In zoology, a sessile animal is one that remains fixed in one place. Such sedentary animals are usually permanently attached to a surface, such as sea anemones, barnacles, limpets, and mussels. The term sessile is also used to describe the eyes of cetaceans that lack stalks and sit directly on the animal's head.
In botany, a sessile structure is one that has no stalk (in cases where one might be expected) and grows directly from a stem. Examples include the acorns and leaves of some oak trees.