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..

3. (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
Muscle layer (from mesoderm)
(c) True coelom (e.g., annelid)
Coelom
Tissue layer lining coelom and suspending internal organs (from mesoderm)
Mesentery
(a) Radial symmetry
(b) Bilateral symmetry

4. 4 3 2 1 Coelom from digestive tube Pseudocoelom True coelom
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
Sponges
Cnidarians
Flatworms
Roundworms
Mollusks
Annelids
Arthropods
Echinoderms
Chordates

5. Includes sessile animals once believed to be plants
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
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. This is the largest group of animals
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..
Muscle segments
Post-anal tail
Notochord
Anus
Dorsal, hollow nerve cord
Pharyngeal slits
Brain
Mouth

20. Lungs or lung derivatives
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. There are three major groups of mammals
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..