All the various types of crustaceans share a common larval stage, called a nauplius larva , which is one of the characteristics uniting that diverse group into a single class. Comparative anatomy also provides proof of evolution. We find the same bones in many different types of animals, but these bones are often modified to do different things. The wing of a bird and the wing of a bat contain exactly the same bones as the arm of a human, but the size, shape, and even internal structure of these bones are all adapted to play a different role in each animal. We call structures like the wings of a bird and the wings of a bat homologous structures .
Homologous structures are structures that are derived from a common ancestor.
Even if they are superficially different, they are developmentally related. Homology does not mean that these structures must share the same function. You can alter the same pieces to make different biological structures. The flippers of a whale are supremely designed to cut through the water, but they are homologous with our own human arms. You can trace out the same bones in each, in the same relative positions, and they develop in roughly the same fashion.