 Some hemichordates also have a tubular nerve cord.In the early embryonic stage, it looks like the hollow nerve cord of chordates.Because of the highly modified nervous system of echinoderms, it is not possible to discern much about their ancestors in this matter, but based on different facts it is quite possible that all the present deuterostomes evolved from a common ancestor that had pharyngeal gill slits, a hollow nerve cord, circular and longitudinal muscles and a segmented body.