The large branches within the Animal Kingdom evolutionary tree are ‘phyla’ (the singular being ‘phylum’). ‘Animal phyla’ outlines thirty three phyla, although there are still disputes and disagreements concerning how many phyla are needed to classify the less well-known species. The most easily recognised are Porifera, Cnidaria, Arthropoda, Nematoda, Annelida, Mollusca, Platyhelminthes, Echinodermata, and Chordata. Animal phyla each comprise a branch of the evolutionary tree and these branches are always connected to other branches. Because of this, some phyla are more closely related to each other than they are to others. This information is vital for understanding how structure, function, and evolution interconnect in the Animal Kingdom.