Phylum Chordata

The Vertebrates

The Phylum Chordata Includes:

1. Subphylum Cephalochordata (=lancelets)2. Subphylum Urochordata (= tunicates)3. Subphylum vertebrata:• Class Agnatha - jawless fish • Class Chondrichthyes - cartilaginous fish• Class Osteichthyes - bony fish• Class Amphibia• Class Reptilia• Class Aves – birds• Class Mammalia

4 main characteristics1. Notochord (develops into backbone in vertebrates)

2. Hollow dorsal nerve chord (develops into brain and spinal chord

3. Pharyngeal slits

4. Muscular, post anal tail

NOTE: NOT all characteristics are seen in all adults – but are present at some point in life cycle

Characteristics Shared by Vertebrates1. Coelomate and deuterostome development

(3 tissue layers in development and mouth forms AFTER anus forms )

2. Bilateral symmetry 3. Endoskeleton - made of cartilage or bone and can support a larger

body • Only phylum to have bones

4. Paired appendages5. High degree of cephalization - well developed head and brain

protected by cranium 6. Closed circulatory system - heart with 2, 3 or 4 chambers 7. Efficient respiratory and excretion system

8. Tube digestive system

9. Advanced reproductive systems

10. An endoskeleton which has two main parts:i. Axial Skeleton: made up of the vertebral column, skull & rib

cage- supports body and protects spinal column,

brain & other internal organs

ii) Appendicular Skeleton: made of the appendage bones and wide flattened girdles to which they are attached

- is attached to axial skeleton- ex. arms, legs

Germ Layers

three embryonic germ layers: endoderm, mesoderm, and ectoderm.

Vertebrates

• Subphylum Vertebrata• Internal jointed skeleton of

vertebrates is living tissue that grows with the animal–Main axis of skeleton consists of vertebral

columns and a skull that encloses the brain• Cephalization is accompanied by sense

organs• Evolution of jaws and predation• Amnion allows reproduction on land

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Vertebrate Features

• Living endoskeleton with vertebral column

• Closed circulatory system• Paired appendages• Efficient respiration and excretion• High degree of cephalization• Adapted to active lifestyles

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Class Agnatha (Jawless Fish)• Aquatic, gill-breathing

vertebrates• Usually have fins and scale-

covered skin• Lack bony skeleton• Lampreys and hagfish are

modern-day jawless fish

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Development of JawsJaws thought to have evolved from first pair of gill arches of agnathans

Class Chondrichthyes - cartilaginous fishClass Osteichthyes - bony fishClass AmphibiaClass ReptiliaClass Aves – birdsClass Mammalia

Class Chondrichthyes (Cartilaginous Fishes)

• a skeleton of cartilage • Lack gill cover (as in bony fishes)• Utilize lateral line system• Filter feeders and predators• Pectoral fins can be enlarged into

large, wing-like fins• Sharks, rays, skates

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Class Osteichthyes (Bony Fishes)

• have a skeleton of bone• Swim bladder– Gas-filled sac in bony fishes– Volume can be altered to change

buoyancy

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Class Amphibia (Amphibians)

• Tetrapods (four limbs)• Hypotheses of tetrapod evolution– Lobe-finned fishes had an evolutionary

advantage due to movement capability– further adaptations promoted by:• Supply of food on land, and• Absence of predators

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Diversity of Amphibians

• Amphibians today occur in three groups:

– Salamanders and newts

• Salamanders practice internal fertilization

– Frogs and toads

• Tailless

– Caecilians

• Legless, sightless, worm-shaped

• Most return to water for reproduction

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Amphibian Features

• Usually tetrapods• Lungs usually present in adults• Metamorphosis• Smooth and moist skin• Three-chambered heart• Ectothermic

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Metamorphosis

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Vertebrate Circulatory Pathways

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Amniotes

• A group of tetrapods having embryos equipped with amnios

• An amnios is a membranous pouch in which the embryo develops• Enabled the evolution of eggs to be laid on land

rather than in water• Seen in reptiles and higher evolutionary

classes• Amniote embryos may be laid as eggs or

carried by the female

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Class Reptilia

• Thought to have evolved from amphibian ancestors

• Practice internal fertilization• Lay eggs protected by a leathery

shell (amniotic egg)

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Anatomy and Physiology of Reptiles

• Reptiles have a thick, scaly skin that is keratinized and impermeable to water– Usually tetrapods– Lungs with expandable rib cage– Shelled amniotic egg– Dry, scaly skin– Ectothermic

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Class Aves(Birds)

• Characteristics of Class Aves– Feathers– Hard-shelled amniotic egg– Four-chambered heart– Often winged– Air sacs– Endothermic

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Class Mammalia(Mammals)

• Mammalian skull accommodates a larger brain relative to body size

• Chief characteristics are hair and milk-producing mammary glands

• Infant dependency• Internal development• Differentiated teeth

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Monotremes and Marsupials

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Mammals

• Monotremes - Hard-shelled amniotic eggs

• Marsupials - Females contain pouch• Placentals - Females have organ for

exchange of maternal and placental blood

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