The phylum name means jointed foot . Jointed appendages is a major characteristic of all members of the phylum. Once it is formed, this hard body covering does not grow. To allow for growth, arthropods have to shed their exoskeleton in a process called molting .
Most arthropods have compound eyes composed of many individual lenses.
In addition to the compound eyes, many arthropods also have single lens, simple eyes that sense light intensity. All arthropods have an open circulatory system . This type of system has a heart and a few major arteries veins. There are very few capillaries connecting the arteries and veins. The blood spills into the body cavity where it is picked up and taken back to the heart.