Question: what is a key difference between the subphylum urochordata and vertebrata?
Answer: In Urochordata,the notochord, nerve cord, and postanal tail is only found in the larval stage. So they don't have these chordate characteristics as adults. In Cephalochordata,notochord is extended in head region and shows throuhout their life. Vertebrates are obviously very different because they have vertebrae.