With over a million species discovered, arthropods are the most numerous of the earth's animals making up about 80% of the total. Representatives include crustaceans, insects and spiders.

Arthropods have a segmented exoskeleton and have reasonably efficient breathing systems. They also have a well developed circulatory, digestive, reproductive and nervous systems with complicated sense organs like antennae and eyes.

There are many classes of Arthropod, but three which are found abundently in water; Crustacea, Insecta, and Arachnida.