 The bottom end of the body is an ampulla (a flask-like swelling in a tube-like structure), which anchors the animal in the tube and enables it to retract its body when threatened, reducing the body to 20 percent of its maximum length.Longitudinal muscles retract the body very quickly, while circular muscles slowly extend the body by compressing the internal fluid.For feeding and respiration each phoronid has at the top end a lophophore, a "crown" of tentacles with which the animal filter-feeds.