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