Stomatopods are very interesting animals. Their name is derived from the first five thoracic appendages that are used in feeding (stomato = mouth; pod = foot). Each of these is subchelate, the second being much larger and used to either stab or strike prey. The barbed shape of the arms of the stabing species resemble those of a praying manits giving rise to the common name "mantis shrimp". The last three pairs of thoracopods are used for walking, and the abdominal appendages, from which the gills arise, can be used for swimming. Although the group is small, less than 400 species, stomatopods are very advanced invertebrates. The striking blow from a large gonodactylid is equivalent to the force produced by a bullet from a .22 caliber short cartridge, and the eyes are the most advanced in the animal kingdom, being tripartite with central band that allows sensitivity to polarized light and a view of nearly 360 degrees in three dimensions. All stomatopods are voracious predators. Species range in size from 2-30 cm.