Chordates (Chap 27)

Kingdom: AnimaliaPhylum: 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