a chordata is a fresh water lobster
"Chordata" is a phylum of animals having a notochord. Generally, the notochord exists at some stage of the animal's development, but it is often replaced with a...
Try looking up sea squirts (Tunicata), acorn worms (Enteropneusta) and Pterobranchia. Oh, and Branchiostoma of course, the lancelet. And in some ways hagfish aren´t considered real vertebrates...