The Ecdysozoa are a grouping of protostome animals, including the Arthropoda (insects, chelicera, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes. A large study in 2008 by Dunn et al. strongly supported the ecdysozoa as a natural grouping. The group is also supported by morphological characters, and can be considered as including all animals that shed their exo… (More on Ecdysozoa)