Crustaceans are a group of arthropods distinguished by the following characters:

• a body divided into cephalothorax and abdomen

• two pairs of antennae and three pairs of mouth appendages

Examples of crustaceans include crabs, pillbugs, and barnacles (It’s true! Under that lumpy exterior, barnacles are crustaceans with all of the right characters!).

Sally Lightfoot Crab photo by Gerald and Buff Corsi © California Academy of Sciences; Acorn Barnacles photo by Sherry Ballard © California Academy of Sciences; Pillbugs photo © 2002 William Leonard