Animal mesoderm forms by enterocoelic pouching, through invagination of the endoderm. The main deuterostome phyla are the Echinodermata and the Chordata. Echinoderms are exclusively marine and include starfish, sea urchins, and sea cucumbers. The chordates are dominated by the vertebrates (animals with backbones), which consist of fishes, amphibians, reptiles, birds, and mammals. The deuterostomes also include the Hemichordata (acorn worms). The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting. They include the largest animal phylum, the Arthropoda, which contains insects, spiders, crabs, and their kin. All of these have a body divided into repeating segments, typically
Branching order of bacterial phyla (Cavalier-Smith, 2002) Branching order of bacterial phyla (Cavalier-Smith, 2002) There are several models of the Branching order of bacterial phyla, one of these was proposed in 2002 and 2004 by Thomas Cavalier-Smith. In this frame of work, the branching order of the major lineage of bacteria are determined based on some morphological characters, such as cell wall structure, and not based on the molecular evidence (molecular phylogeny). Whereas modern molecular studies point towards the root of the tree of life being between a monophyletic Bacteria and Archaea+Eukarya (Neomura), in the Cavalier-Smith theory, the last common ancestor (cenansestor) was a Gram-negative diderm bacterium