Mostly possessing branched .

The branched appendages seen with crustaceans are termed , contrasting the appendages associated with, for example, insects. Crustaceans also display a form at some point in their life cycles during which they use their to swim and, at the same time, possess only a single .

The crustaceans can be differentiated into a number of distinct types including copepods, decapods, and isopods. Note, however, that not all aquatic arthropods are crustaceans, with the notably not.