Open circulatory systems are found in mollusks, arthropods and several other invertebrates. Open circulatory systems work by pumping blood into a hemocoel, which in turn diffuses blood and pumps it back into the circulat... More »

All vertebrates, segmented worms, such as earthworms, and cephalopods, such as squid, have closed circulatory systems. Closed circulatory systems allow larger animals to be much more active than those with open circulato... More »

The blood circulatory system transports nutrients and oxygen throughout the body. The system is comprised of the heart and blood vessels. More »

Animals with exoskeletons include all arthropods such as insects, crustaceans and spiders as well as many other invertebrate animals such as shelled mollusks. Shelled mollusks include snails, tusk shells, clams, nautilus... More »

All mollusks have a common ancestor in the annelid worm, are primarily aquatic animals, have soft bodies, have hard shells (the exoskeleton), have a mantle (thin tissue) and have an open circulatory system. Mollusks incl... More »

In the rain forest, arthropods are known to lay their eggs in the feces of sloths, providing food for the growing larvae. This is a perfect example of commensalism. More »

The common characteristics of arthropods are they are invertebrates, which means they lack backbones. In fact, they lack bones of any kind but possess a protective exoskeleton, which they molt in order to grow and repair... More »