In addition, this species also lacks a notochord. Therefore, it should be clear why these species are called Hemichordates, and arc not included with the true chordates. There are four distinctive derived characteristics of chordates that distinguish them from ancestors. B. Hollow nerve cord that lies dorsal to the notochord. The next group, the Tunicata, is included as part of the true chordates, and represent some of the most primitive ancestors of the Subphylum Vertebrata.
Tunicates differ strongly in appearance between the adult and the larva.
The larval form possesses more of the chordate characteristics than the adult form. Larval stage lasts only a few days, and ends when the larva attaches to a substrate and metamorphoses into an adult. This example should illustrate to you that although chordates are said to have four basic things in common, these characteristics need not be retained throughout life for an animal to be considered a chordate. Amphioxus are 2-3 inches in length, and live on seashores throughout the temperate zone. Fish-like in appearance, it has a laterally compressed dorsal fin, but it does not have complete organs, or any bony structures.