What animals are not arthropods?

Because Arthropoda is a phylum, one need only look for any other animal phylum to find non-arthopods. Chordates for example, mammals, fish, birds. Mollusca, with slugs, snails, squid, octopi. Echinoderms, like sand dollars and starfish. Annelida, with earthworms, leeches, and so on. Chances are, if there's an animal which doesn't have a chitin exoskeleton, you've found something not an arthropod.