Scientists are interested in the evolutionary history of animals and the evolutionary relationships among them. There are three main sources of data that scientists use to create phylogenetic evolutionary tree diagrams that illustrate such relationships: morphological information (which includes developmental morphologies), fossil record data, and, most recently, molecular data. The details of the modern phylogenetic tree change frequently as new data are gathered, and molecular data has recently contributed to many substantial modifications of the understanding of relationships between animal phyla.
clade of protostomes that exhibit exoskeletal molting (ecdysis)
group of animals with true differentiated tissues
clade of protostomes that exhibit a trochophore larvae stage or a lophophore feeding structure
group containing all animals
group of animals without true differentiated tissues