noun, plural: haemocoels
In most vertebrates the oxygen is supplied to different organs of the body through capillaries in a closed circulatory system. In many invertebrates, the oxygen is supplied directly to the organs. That is, the hemolymph circulates through the haemocoel and bathes the organs directly to supply them with oxygen.
Word origin: from haemo- + Latin coel, from Greek koilos (hollow)