Earth and Environmental Sciences Invertebrate Paleontology Fall 1999 November 15. The jointed appendages are used for walking and swimming and modified to form mouth parts, accessory reproductive parts. Muscles attached to the exoskeletons flex and move the jointed, armored body.
More primitive arthropods have a large number of similar segments.
Other segments have one or two pairs of appendages used for locomotion. The head is composed of 6 fused segments with the appendages on segments 3 through 6 modified for mouth parts. The protein varies in composition, producing skeleton of varying flexibility. During molting the softer inner layer is resorbed and the materials are reused by the epidermal cells to secrete the new skeleton. Those who insist the diversity is too great to have a common origin raise the various superclasses to phylum status.