The arthropods, or crustaceans, were the ancestors of the first vertebrates. The forerunners of the fish family were two modified arthropod ancestors.  Air-breathing amphibians developed from the arthropods, whose swim bladders had evolved into lungs. 
The brachiopods early reached their climax, being succeeded by the arthropods, and barnacles made their first appearance. 110 millions years ago crabs, lobsters, and the modern types of crustaceans matured.  The trilobites existed in tens of thousands of patterns and were the predecessors of modern crustaceans.