Any of the small marine animals belonging to the phylum Hemichordata or to either of the chordate subphyla Urochordata and Cephalochordata, characterized (at some point in the life cycle) by a hollow dorsal nerve cord, a notochord, and gill slits; a hemichordate, urochordate, or cephalochordate, or a hypothetical ancestral form of any of these.

Of or designating a protochordate.