NextPrevious

Anatomy: Animals Inside

Circulatory System

Do all animals have blood?

Some invertebrates, such as flatworms and cnidarians, lack a circulatory system that contains blood. These animals possess a clear, watery tissue that contains some phagocytic cells, a little protein, and a mixture of salts similar to seawater. Invertebrates with an open circulatory system have a fluid that is more complex and is usually referred to as hemolymph (from the Greek term haimo, meaning “blood,” and the Latin term lympha, meaning “water”); their hemoglobin is not concentrated in cells within the hemolymph, but rather is found floating in the hemolymph. Invertebrates with a closed circulatory system have blood that is contained within blood vessels. Other examples of circulatory systems are found in squids, octopi, and crustaceans—animals that also have oxygen-carrying molecules in their plasma, but their bodies use a copper-based molecule hemocyanin to carry oxygen instead.



Close

This is a web preview of the "The Handy Biology Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App