The dorsal, hollow nerve cord of a chordate embryo develops into the central nervous system - the brain and spinal cord. The digestive tube of chordates extends from the mouth to the anus. The region just posterior to the mouth is the pharynx, which opens to the outside of the animal through several pairs of slits. These pharyngeal slits allow water that enters the mouth to exit without continuing through the entire digestive tract. The pharyngeal slits function as suspension-feeding devices in many invertebrate chordates.
Most chordates have a tail extending posterior to the anus.
By contrast, most nonchordates have a digestive tract that extends nearly the whole length of the body. The chordate muscular, postanal tail contains skeletal elements and muscles and provides much of the propulsive force in many aquatic species. Phylum Hemichordata - the acorn worms. 1. pharyngeal slits 2. This is one group of invertebrate chordates that provides clues to the origin of vertebrates.