BIO 301M Lecture Notes - Lecture 1: Dorsal Nerve Cord, Agnatha, Gnathostomata
Document Summary
Chapter 25: chordates: chordates- animals with an embryo that has a notochord, dorsal nerve cord, bilateral symmetry, coelomate animals, pharyngeal gill slits, and a tail that extends beyond the anus, ex. Lancelet or a vertebrae: most of 50,000 chordates are vertebrates, animals with a backbone. Jawless fish had external bony plates that covered head and sometimes body and was used to fend off predators=ostracoderms. They became extinct when jawed fish arose: lempreys are cylindrical in shape, is parasitic and goes through metamorphosis, hag fishes are cylindrical in shape and are bottom-feeders who rely on senses because of their poor eyesight. They became extinct by the end of the. Devonian period: aconthodians did not have a bony armor, were less diverse and more smaller than placoderms and became extinct at the end of the permian period, cartilaginous fishes- jawed fish that has a skeleton of cartilage. They have gill slits hidden beneath a gill cover.
