Gastrovascular system of small hydromedusae: mechanisms of circulation

Small medusae possess a circulatory system of narrow tubes subdivided into several compartments by functional "sphincters." Flow is activated by gastrodermal flagella twice as long as the diameter of the tubes. The flow may be reversed in any part of the system through pressure waves generated by muscular action of the gastric pouches. The combination of flagellar and muscular action provides an adjustable, low-pressure circulation.