Chordata
Chordata is the phylum that everybody is most familiar with. For something to be a chordata it must have...
pharyngeal slits - a series of openings that connect the inside of the throat to the outside of the "neck". These are often, but not always, used as gills.
dorsal nerve cord - a bundle of nerve fibers which runs down the "back". It connects the brain with the lateral muscles and other organs.
notochord - cartilaginous rod running underneath, and supporting, the nerve cord.
post-anal tail - an extension of the body past the anal opening.