Zoo Disc will follow the classification schemes constructed using phylogenetic
systematics (cladistics). It is important to point out that some of the groups recognized by traditional taxonomists may not valid
from a cladistic standpoint. For a group to be a valid taxon (clade) according to phylogenetic systematics it must be monophyletic, that is, the group must contain the most recent ancestor of the group and all the descendants of that ancestor. A paraphyletic group is one that includes the most common ancestor of the group but not all of the descendents of that ancestor. For example, the reptiles do not form a valid cladistic taxon since they are a paraphyletic group (the ancestor of the reptiles is also the ancestor of the birds and mammals)! You should also realize that taxonomy is a dynamic science that seeks to unravel the evolutionary relationships among organisms that are themselves dynamic and evolving. As new information becomes available, taxonomic groupings may change.
What is probably most important is to gain an understanding of the characteristics (form and function) that define the various animal groups so that they can be recognized and appreciated.