Urochordates, commonly known as tunicates, differ from other chordate subphyla (Cephalochordata and Vertebrata) in that the adult form has no notochord, nerve cord, or tail. In fact, an adult tunicate is an immobile, filter-feeding marine animal that in some ways looks more like .
Urochordates have a sparse fossil record. A Precambrian fossil known as Yarnemia has been referred to the Urochordata, but this assignment is doubtful. Complete body fossils of tunicates are rare, but tunicates in some families generate microscopic spicules that may be preserved as microfossils. Such spicules have occasionally been described from Jurassic and later rocks.
Chapter 34 (Exam 2) STUDY. PLAY. Which of the following is a characteristic of all chordates at some point during their life cycle? A) jaws B) post-anal tail C) four-chambered heart D) vertebrae. B) post-anal tail. Why do adult urochordates (tunicates) lack notochords, even though larval urochordates have them? Larvae use notochords to _____.