Key Morphologic Features

The name arthropod means “jointed foot” (arthro means “joint,” and pod means “foot”). All adult arthropods have jointed appendages. All arthropods are covered with a chitinous exoskeleton that is composed of segments. Chitin is a hard (yet elastic) body covering that envelops the entire body of all arthropods. Whenever you step on a cockroach, the chitin makes the “crunch” sound. Arthropods have a hemocoel, a body cavity filled with hemolymph. Hemolymph is a bloodlike fluid that bathes the internal organs of an arthropod. When a flying insect hits the windshield of a speeding car and “splats,” hemolymph is the fluid that creates the “splat.” Arthropods have a very simple circulatory system composed of a heartlike dorsal tube. This dorsal tube is actually a primitive heart that pumps the hemolymph to the arthropod’s head. The digestive system of arthropods begins with a ventral mouth and ends with a terminal anus. Arthropods possess a variety of respiratory systems; they may use gills, book lungs, or tracheal tubes as respiratory organs. Arthropods have complex nervous and excretory systems. However, the most important organ system of the arthropods is the reproductive system. Arthropods have separate sexes; they are dioecious. Reproduction is by means of eggs. Arthropods have a tremendous reproductive capacity.