We divide them into subphylums. Trilobites and many other extinct animals are on their own. Crabs, spiders, mites, and scorpions are chelicerates. Chelicerae are distinct appendages above and in front of their mouths. that look like jaws or pincers. Millipedes and centipedes are myriapods; that is, they are many footed. Lobsters, crabs, crayfish, shrimp, and barnacles are crustaceans. They have biramous appendages; that is, their legs branch in two. Insects have six unbranched legs; therefore, we call them hexapods.