Answer the following question given this paragraph: 

Living species of chordates are classified into three major subphyla: Vertebrata, Urochordata, and Cephalochordata. Vertebrates are all chordates that have a backbone. The other two subphyla are invertebrate chordates that lack a backbone.


Q: Living species of chordates are classified into three major subphyla: vertebrata, urochordata, and what?


A:
cephalochordata