 The lophotrochozoans are grouped on a basis of molecular similarities, are named for the feeding apparatus called a lophophore of some phyla in the group and for the trochophora larva found in molluscs and annelids. The ecdysozoans include the nematodes and the arthropods. Both of these phyla have exoskeleton that must be shed for the animal to grow. This molting process is called ecdysis, the basis for the name ecdysozoan. | An animal phylogenetic tree is a work in progress. A revised phylogenetic tree based on molecular data distinguishes two protosome clades: the lophotrochozoans and the ecdysozoans  |
The genes that build animal bodies are ancient. Changes in the regulation of homeotic gene expression have been significant factors in the evolution of animal diversity.
