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 characteristics

1. 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 Vertebrates 1. 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 appendages 5. 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 8

Vertebrate Features

• • • • • • Living endoskeleton with vertebral column Closed circulatory system Paired appendages Efficient respiration and excretion High degree of cephalization Adapted to active lifestyles 9

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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 10

Development of Jaws

Jaws thought to have evolved from first pair of gill arches of agnathans Class Chondrichthyes - cartilaginous fish Class Osteichthyes - bony fish Class Amphibia Class Reptilia Class Aves – birds Class 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 12

Class Osteichthyes (Bony Fishes)

• • have a skeleton of bone Swim bladder – Gas-filled sac in bony fishes – Volume can be altered to change buoyancy 13

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 14

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 15

Amphibian Features

• • • • • • Usually tetrapods Lungs usually present in adults Metamorphosis Smooth and moist skin Three-chambered heart Ectothermic 16

Metamorpho sis

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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 19

Class Reptilia

• • • Thought to have evolved from amphibian ancestors Practice internal fertilization Lay eggs protected by a leathery shell (amniotic egg) 20

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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 21

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Class Aves (Birds)

Characteristics of Class Aves – Feathers – – – – – Hard-shelled amniotic egg Four-chambered heart Often winged Air sacs Endothermic 22

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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 23

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 25