ABBOTTSCOLLEGE 1 Page 81

CHORDATES  Animals that have a backbone  Most advanced type of animal

PHYLUM CHORDATA 3  An extremely successful group of animals  Occupy a wide range of habitats  Have:  Bilateral symmetry  Cephalisation  Triploblastic tissue layers  Segmented body  Well developed coelom  Through gut

CHARACTERISTICS OF CHORDATES  All chordates have:  Notochord  Hollow, dorsal, tubular nerve cord  Pharyngeal (gill) slits  Post-anal tail PAGE 81

NOTOCHORD  Rod-like support  Present in basic and developing chordates  Normally replaced later in life by the vertebral column  First type of backbone support in evolution

DORSAL NERVE CHORD  Beginnings of a spinal chord  Forms the brain at one end  Remains present, but becomes modified in most chordates

PHARYNGEAL SLITS  Appear in development of all chordates  Disappear in terrestrial animals  Remain present in fish

POST-ANAL TAIL  A muscular structure that extends beyond the anus.  This may remain present all through life, but often disappears as the animal matures.

CLASSIFICATION OF CHORDATA  Phylum includes over species  3 Subphyla  Subphylum Urochordata e.g. Sea Squirts  Subphylum Cephalochordata e.g. Amphioxis  Subphylum Vertebrata e.g. Fish, birds, mammals, reptiles and amphibia The first two subphyla are made up of A very few primitive aquatic marine forms Do not have vertebrae

SUB-PHYLUM:VERTEBRATA

CHARACTERISTICS OF VERTEBRATES 11 An endoskeleton of cartilage and/or bone A notochord that forms a vertebral column made up of cartilagenous or bony vertebrae Two pairs of appendages (fins or limbs) attached to girdlesExtracellular (outside the cells) digestion in a complex digestive tractA closed circulatory systemMay be ectotherms or endotherms Ectotherms get their body heat from their surroundings Eg fish, amphibians, reptiles

CLASSES OF VERTEBRATES AgnathaCondrichthyesOsteichthyesAmphibiaReptiliaAvesMammalia PAGE 82

CLASS AGNATHA Most primitive marine vertebrates Jawless Fish Cartilaginous Skeleton e.g. lamprey, hagfish Notochord throughout life

CLASS CONDRICHTHYES Aquatic (mostly marine) Cartilaginous Skeleton No Swim bladder e.g. sharks, rays, skates 5 pairs gill slits

CLASS OSTEICHTHYES All aquatic (marine and fresh water) Bony skeleton 4 pairs gill slits covered by an operculum e.g. salmon, yellowtail, galjoen Swim bladder

CLASS AMPHIBIA Aquatic and TerrestrialSimple lungsSmooth moist skinEctotherms Need water for reproduction e.g. frogs, toads, salamander Undergo metamorphosis

CLASS REPTILIA Mainly terrestrial, Dry skin with scales Internal fertilisation Ectotherms, e.g. snakes, lizards, crocodiles, tortoises, turtles Lay eggs with soft leathery shells

CLASS AVES AKA BirdsBody covered in feathers Forearms adapted to wings Endothermic Lay eggs with a hard calcareous shell Toothless jaws covered by a beak e.g. eagles, doves, ducks, penguins, sea gulls Gaseous exchange assisted by air sacs

CLASS MAMMALIA All mammals share 3 unique characteristics Three middle ear bones Body Hair Production of milk through mammary glands All are endotherms Different types of mammals: Monotremes Egg laying mammals (e.g. duck-billed platypus) Marsupials Young develop in a pouch (e.g. kangaroo) Placentals Give birth to well developed young, have a placenta (humans, cows, whales, lions etc.)

MONOTREME 20

MARSUPIAL 21

PLACENTALS 22

TO DO 23 PAGE 83LEARNING ACTIVITY 4EVOLUTION OF THE CHORDATES

DEFINITIONS: Notochord: A rod like structure that, in more developed chordates, develops into the vertebral column. Dorsal Nerve Chord: A tubular nerve chord that persists through life, forming part of the brain stem. Pharyngeal Slits: Used for separation of water and air to allow breathing underwater. (AKA Gills) Post Anal Tail: The body of the organism extends past the anus.Endoskeleton: A skeleton housed inside the body. Extracellular Digestion: Digestion taking place outside a cell in a specialised organ Closed Circulatory System: The blood circulates the body and is confined to blood vessels.

DEFINITIONS: Swim Bladder: A gas-filled sac present in the body of many bony fishes, used to maintain and control buoyancy. Ectothermic: An animal that is dependent on external sources of body heat. (AKA Cold Blooded) Endothermic: An animal that can generate internal heat (AKA warm-blooded)Internal Fertilization: The fertilization of a gamete inside the body Air Sacs: The extension of a bird’s lung cavity into the bones or other parts of the body, these fill with air and aid in flight. Middle Ear Bones: 3 small bones in the inner ear that form an important part of our ability to hear.

THE END