As the below phylogenetic diagram suggests, the invertebrate deuterostomes comprise approximately 10,000 species of marine animals distributed throughout the oceans of the world. Recent molecular phylogenetic studies suggest that the deuterostomes include only the echinoderms, hemichordates, and chordates. As the below tree diagram illustrates, the majority of animals more complex than jellyfish and other Cnidarians are split into two groups, the protostomes, and deuterostomes. As the below image graphically represents, a phylogenetic tree is a branching diagram or a tree showing the evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical or genetic characteristics.
