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Chapter 17 - The Evolution of Animals

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... researchers must depend on clues from comparative anatomy and embryology Four key evolutionary branch points have been hypothesized Presence or absence of true ... – PowerPoint PPT presentation

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Title: Chapter 17 - The Evolution of Animals


1
Chapter 17 - The Evolution of Animals
  • What Is an Animal?
  • Are eukaryotic, multicellular, heterotrophic
    organisms that obtain nutrients by ingestion
  • Digest their food within their bodies..

2
Animal Phylogeny
  • To reconstruct the evolutionary history of animal
    phyla, researchers must depend on clues from
    comparative anatomy and embryology
  • Four key evolutionary branch points have been
    hypothesized
  • Presence or absence of true tissues
  • Radial or bilateral symmetry
  • Presence or absence of a body cavity (coelom)
  • Mechanism of coelom formation..

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  • Phylum Porifera
  • Includes sessile animals once believed to be
    plants
  • Lack true tissues
  • Resembles a sac perforated with holes (pores)
  • Draws water into a central cavity, where food is
    collected..

6
  • Phylum Cnidaria
  • Characterized by organisms with radial symmetry
    and tentacles with stinging cells (cnidocytes)
  • Sac body plan with a gastrovascular cavity
  • Do not have true organs
  • Life cycle includes two body forms
  • Sessile polyp
  • Floating medusa..

7
  • Cnidarians are carnivores that use tentacles
    armed with cnidocytes, or stinging cells, to
    capture prey..

8
  • Phylum Platyhelminthes
  • Is represented by the simplest bilateral animals
  • Have true organs but no body cavity acoelomate
  • Digestive tract is two directional only one
    opening incomplete digestive tract
  • Includes free-living forms such as planarian
  • Includes many parasitic forms such as tapeworms
    and flukes..

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  • Phylum Nematoda
  • exhibit an important evolutionary adaptation a
    digestive tube with two openings, a mouth and an
    anus
  • A complete digestive tract can process food and
    absorb nutrients efficiently
  • Only phylum with a pseudocoelom..

12
  • Phylum Mollusca
  • Is represented by soft-bodied animals, but most
    are protected by a hard shell
  • All have a similar body plan
  • Muscular foot maybe modified into tentacles
    for locomotion and defense and food gathering
  • Mantle secretes shell and aids in respiration
  • Visceral mass containing internal organs
  • First group with a true coelom eucoelomates..

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  • Phylum Annelida
  • Includes worms with body segmentation division
    of the body along into length into a series of
    repeated segments look like rings..

16
  • Phylum Arthropoda
  • All have exoskeleton of chitin
  • Appendages are jointed
  • Appendages are highly specialized for the
    environment
  • Undergo metamorphosis change in body form
    during development
  • This is the largest group of animals
  • Includes insects most abundant animals..

17
Metamorphosis egg ? larva ? pupa ? adult..
18
  • Phylum Echinodermata
  • Is named for the spiny surfaces of the organisms
  • Have endoskeleton
  • Have water-vascular system hydraulic pumps that
    circulate water for gas-exchange, waste disposal,
    circulation of nutrients, and locomotion with
    tube feet
  • All aquatic..

19
  • Phylum Chordata all possess these characters at
    some point during development
  • Have notochord supporting rod of tissue
    becomes vertebrae in one subphylum
  • Have dorsal, hollow nerve cord
  • Have post-anal tail
  • Have pharyngeal pouches..

20
Chordate Evolution
21
  • The subphyla include the invertebrate chordates
    lancelets (cephalochordata) and tunicates
    (urochordata), which also share four key chordate
    characteristics..

22
  • This phylum includes the subphylum Vertebrata
  • The notochord develops into the vertebral column..

23
  • The first three major classes of the phylum are
    fishes
  • Agnatha jawless fishes, eg. lampreys
  • Chondrichthyes cartilage fishes
  • Osteichthyes bony fishes..

24
  • Cartilaginous fishes have a flexible skeleton
    made of cartilage the only bone is found in the
    jaw
  • Includes sharks, rays, and skates..

25
  • Bony Fish
  • Have a skeleton reinforced by hard calcium salts
  • Have a lateral line system, a keen sense of
    smell, and excellent eyesight
  • Most bony fishes are ray-finned fishes
  • A second evolutionary branch includes lungfishes
    and lobe-finned fishes..

26
  • Terrestrial vertebrates are collectively called
    tetrapods, which means four legs
  • Class Amphibia
  • Exhibit a mixture of aquatic and terrestrial
    adaptations
  • Usually need water to reproduce..

27
  • Class Reptilia - can live totally on land
  • Have scales to prevent dehydration
  • Have claws for digging and protection
  • Have lungs for breathing
  • First group to develop the amniotic egg..

28
  • Class Aves
  • Evolved the ability to fly and only animals with
    feathers
  • Bird anatomy and physiology are modified for
    flight
  • Bones are honeycombed, which makes them lighter
  • Some specific organs are absent, which reduces
    weight
  • A warm, constant body temperature is maintained
    through endothermy..

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  • Class Mammalia
  • Includes mostly terrestrial organisms
  • Have hair
  • Have mammary glands that produce milk and nourish
    the young
  • There are three major groups of mammals
  • Monotremes lay eggs
  • Marsupials do not have a placenta
  • Eutherians (placental mammals) have placenta to
    nourish young inside mothers body..

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