The invertebrate circulatory system varies widely among different species, as invertebrates lack a backbone. Many invertebrates, like earthworms, have a closed circulatory system, where blood is contained within vessels. This system allows for efficient transport of nutrients and oxygen throughout the body. Other invertebrates, such as jellyfish and octopuses, possess an open circulatory system. In this system, blood flows freely through cavities, bathing organs directly. This method is generally less efficient but works well for these organisms, allowing them to thrive in diverse environments.