What some chordates such as sea squirts and lancelets do not have?

Chordates are a phylum of animals that are characterized by having a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some point during their life cycle. Sea squirts and lancelets are two types of chordates that do not have a backbone. Sea squirts are sessile animals that live in the ocean, and lancelets are small, fish-like animals that live in the sand.