The chordata are simply defined as organisms that have a notochord (at least at some stage in their life). Basic support for an organism is provided by this cartilaginous structure. In many organisms, it may develop into vertebrae, presenting the idea that it is a primitive back bone. However, also present in this Phylum are the Tunicates, which appear to be just a simple sac. Only during their free swimming larval stage, they also possess a Notochord, but lost it once they mature.
You can find a list of all of the groups of chordates found in The Great Barrier Reef Marine Park, below.
Class – Next level of classification, grouping animals with similar characteristics