The phylum Vertebrata: a case for zoological recognition

Subphylum Vertebrata of the phylum Chordata. a Key reports that led to the concept of the phylum Chordata. Terms in red are of phylum rank and those in black are of subphylum rank. Those in green were recognized as invertebrates at the times indicated in the first column. b Traditional view (upper) and c our proposed view (lower) of chordate phylogeny with respect to inter-phylum relationships. The proposed phylogeny regards the Cephalochordata, the Urochordata, and the Vertebrata as separate phyla, rather than as subphyla. (modified from [17]