An open circulatory system is a type of circulatory system where blood, or hemolymph, is not confined to vessels but instead flows freely through cavities in the body, allowing it to directly bathe the organs. This system is characteristic of many invertebrates, including those in the superphylum Lophotrochozoa, such as molluscs and annelids, which rely on this fluid-filled space to facilitate gas exchange and nutrient transport.
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