CIRCULATORY SYSTEM

Annelids have a closed circulatory system and circulate the necessary nutrients, blood and gases, through a series of closed vessels. The two main vessels that are used to circulate are known as the dorsal and ventral blood vessels.

Mollusks have a an open circulatory system where blood doesn't fully circulate though the organism. The blood is released from the heart to the vital areas once it has collected the oxygen that the gills have extracted from water. Cephalopod mollusks, such as octopuses and squids, have a closed circulatory system.

Arthropods have segmented bodies as well as an exoskeleton. They include animals such as insects, arachnids, and crustaceans. Arthropods have an open circulatory system. This system consists of a dorsal heart and arteries.

All vertebrate animals have closed circulatory system, consisting of a heart and vascular and lymphatic systems through which a fluid is continuously circulated. All vertebrates have a muscular heart.

In humans, the left lung is smaller than the right lung to make room in the chest cavity for the heart.

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