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Chapter 17 - The Evolution of Animals What Is an Animal? Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion – Digest.

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Presentation on theme: "Chapter 17 - The Evolution of Animals What Is an Animal? Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion – Digest."— Presentation transcript:

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 1.Presence or absence of true tissues 2.Radial or bilateral symmetry 3.Presence or absence of a body cavity (coelom) 4.Mechanism of coelom formation..

3 (a) Radial symmetry (b) Bilateral symmetry (a) No body cavity (e.g., flatworm) Body covering (from ectoderm) Digestive tract (from endoderm) Tissue-filled region (from mesoderm) (b) Pseudocoelom (e.g., roundworm) Pseudocoelom Digestive tract (from endoderm) Body covering (from ectoderm) Muscle layer (from mesoderm) (c) True coelom (e.g., annelid) Coelom Digestive tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Mesentery

4 Multicellularity True tissues Radial symmetry Bilateral symmetry No body cavity Body cavities Pseudocoelom True coelom Coelom from cell masses Coelom from digestive tube 1 2 3 4 SpongesCnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Chordates

5 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.. Pores Water flow Skeleton fiber Central cavity Choanocyte Amoebocyte Choanocyte in contact with an amoebocyte Flagella

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.. Mouth/anus Tentacle Gastrovascular cavity Tentacle Mouth/anus Medusa Polyp

7 Cnidarians are carnivores that use tentacles armed with cnidocytes, or “stinging cells,” to capture prey.. Tentacle Coiled thread Capsule “Trigger” Discharge of thread Cnidocyte 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..

9 Digestive tract (gastrovascular cavity) Nerve cords Mouth Eyespots Nervous tissue clusters

10 Reproductive structures Head Hooks Sucker

11 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..

13 Mantle Mantle cavity Shell Anus Gill Foot Nerve cords Visceral mass Kidney Coelom Heart Reproductive organs Digestive tract Radula Mouth


15 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 Muscle segments Post-anal tail Notochord Anus Dorsal, hollow nerve cord Pharyngeal slits Brain Mouth 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 Eras Cenozoic Mesozoic Paleozoic Precambrian Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Tunicates Lancelets Agnatha (jawless vertebrates, such as lampreys) Chondrichthyes (sharks and rays) Osteichthyes (bony fishes) Amphibia (frogs and salamanders) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Ancestral chordate Vertebrae Jaws Lungs or lung derivatives Legs Amniotic egg Hair Feathers Chordates Vertebrates Tetrapods Amniotes Periods 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..

29 Airfoil

30 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 mother’s body..


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