Chordata. Deuterstome coelomates Four features characterize: Dorsal, hollow nerve cord Develops from ectoderm > develops into CNS: brain and spinal chord Notochord Fluid-filled cells encased in stiff, fibrous tissue Pharyngeal slits/pouches Filter feeding Postanal tail
Notochord develops into the nucleus pulposus in invertebral disks
Haikouella – 530 million years old (Cambrian explosion), 3-cm-long; suspension feeder; resembled craniates in that it had a small brain, eyes, and muscular segments, tooth-like denticles. Did not have a skull.
Haikouichthys – had a skull made of cartilage. Classified as a true craniate.
Vertebrate skeleton evolved as a structure made of unmineralized cartilage