Chordates (Chap 27)

Kingdom: Animalia Phylum: Chordata (evolved ~535 mya) All chordates have the following features at some point in their life (may only be present in the embryo): pharyngeal slits - a series of openings that connect the inside of the throat to the outside of the "neck". These are often, but not always, used as gills. dorsal nerve cord - a bundle of nerve fibers which runs down the "back". It connects the brain with the lateral muscles and other organs.

notochord - cartilaginous rod running underneath, and supporting, the nerve cord. post-anal tail - an extension of the body past the anal opening.

Subphylum: Vertebrata (evolved ~ 500mya) Characteristics have vertebral columns (backbones) brain enclosed in a cranium ventral heart gills or lungs two-- pairs of limbs, eyes, kidneys, sexes

7 Living Classes of Vertebrates 1. Agnatha marine animals lack jaws and paired fins skeletons of cartilage ~ 75 sp. -- hagfish and lampreys

2. Chondrichthyes fishes with skeletons of cartilage skin is placoid scales– miniature teeth embedded in the skin ~ 700 sp. -- sharks, skates and rays

3. Osteichthyes “bony fishes” have a swim bladder have an operculum, a flap on each side of the fish that covers the gills over 29,000 species

4. Amphibia most develop and reproduce in water have primitive lungs moist skin for gas exchange ~ 5700 sp. -- frogs, salamanders…

5. Reptilia scales well-developed lungs most are terrestrial internal fertilization a leathery amniotic egg- embryo surrounded by a fluid-filled sac and membranes ~ 6500 sp. -- turtles, snakes, lizards…

6. Aves light and strong skeleton beak, no teeth feathers large yolked, hard-shelled eggs enlarged sternum where flight muscles can attach ~ 9000 sp.

7. Mammals