Introduction to Animals

1. Introduction to Animals Development, Symmetry, Tissues, Classification AP Biology Unit 6

2. Defining Characteristics of Animals • Multicellular • Heterotrophs • Sexual reproduction followed by development of body tissues and organs from layers of embryonic tissue Slide 2 of 23

3. Animal Development • Following fertilization, animal embryos develop in a systematic fashion Slide 3 of 23

4. Animal Development • Cleavage • A series of rapid cell divisions • No time for cells to grow in between divisions • Gastrulation • Formation of layers of tissue that eventually develop into body parts and organs Slide 4 of 23

5. Body Symmetry • 3 different categories of body symmetry • No symmetry (Asymmetrical) • Ex. Sponges (Porifera) • Radial symmetry • Bilateral symmetry Slide 5 of 23

6. Radial Symmetry • One main axis in the center • No left or right sides– dividing the animal along any axis makes it a mirror image on each side. • Ex. Sea Anemones, Cnidarians (jellyfish) Slide 6 of 23

7. Bilateral Symmetry • Has a left and right side– only one plane will divide the animal so that the two sides are mirror images of one another. • Ex. Humans, fish, insects (most animals have bilateral symmetry) Slide 7 of 23

8. Directional Terms • There are certain directional terms that can be associated with bilateral symmetry • Dorsal = top side (think dorsal fin on dolphins) • Ventral = bottom side • Anterior = the end towards the head • Posterior = the end towards the tail Slide 8 of 23

9. Embryonic Germ Layers • Adult body parts develop from embryonic germ layers • There are 3 different germ layers • Ectoderm • Mesoderm • Endoderm Slide 9 of 23

10. Ectoderm • Outermost layer • Develops into skin, nervous system, sensory organs Slide 10 of 23

11. Mesoderm • Middle layer • Develops into muscles, bones, circulatory system, excretory system, most of reproductive system • Not all animals have mesoderm Slide 11 of 23

12. Endoderm • Inner most layer • Develops into the digestive system, respiratory system Slide 12 of 23

13. Diplo or triplo? • Not all animals have all 3 germ layers • Diploblastic = only have 2 germ layers (no mesoderm, only endoderm and ectoderm) • Ex. Cnidarians (jelly fish) • Triploblastic = have all 3 germ layers • All bilaterally symmetrical animals (worms, birds, mammals, etc) • Closely linked to cephalization (concentration of nervous system and sensory organs close to head region) Slide 13 of 23

14. Body Cavities • Most animals have a body cavity (fluid filled space) between the endoderm and ectoderm • Coelom = body cavity lined with mesoderm • Type of body cavity influences how the animal moves Slide 14 of 23

15. Types of Body Cavities • Acoelomate • Lack an enclosed body cavity • Instead, the space is filled with cells • Ex. Flatworm Slide 15 of 23

16. Types of Body Cavities • Pseudocoelomate • Have a fluid filled space in which many organs are suspended • Only one side (outer side) is lined with mesoderm (muscle) • Can’t control body shape as well since only one layer of muscle • Ex. Roundworm Slide 16 of 23

17. Types of Body Cavities • Coelomate • Have a coelom – body cavity lined with mesoderm on both sides • Better control over movement since there are more muscles present (usually going in several different directions) • Ex. Earthworm, humans Slide 17 of 23

18. Protostomes vs. Deuterostomes • Excluding sponges, cnidarians and ctenophores, all other animals can be classified as either a protostome or a deuterostome. • Classification has to do with how the embryo develops. • Early in development a cavity forms • Blastopore = opening to the cavity Slide 18 of 23

19. Protostomes • Blastopore becomes the mouth of the animal (means “mouth first” in Greek) • Cleavage • Spiral = cleavage occurs in planes diagonal to the vertical • Determinate = The “fate” of each cell is determined very early • Examples include: molluscs, annelids (earthworms), arthropods Slide 19 of 23

20. Deuterostomes • Blastopore becomes the anus (means “mouth second” in Greek) • Cleavage • Radial = cleavage occurs along lines that are parallel or perpendicular to the vertical • Indeterminate = the “fate” of each cell is not determined until a little later (early cells can still become any type of cell– “stem cells”) • Examples include: Echinoderms, Chordates (have a backbone) Slide 20 of 23

21. Animal Classification • Based on developmental morphology • Molecular evidence suggests that this classification may not be entirely accurate • Common ancestor of all animals is thought to be a colonial protist with a flagella Slide 21 of 23

22. Animal Classification • “Basal” animal = porifera (sponge) = simplest animal; at the bottom of the evolutionary tree • Most animals have bilateral symmetry • All animals are thought to belong to a group called Metazoa Slide 22 of 23

23. Scientific Names for Animals • Porifera = sponges • Cnidarians = jellyfish • Platyhelminthes = flatworms • Nematodes = roundworms • Annelids = Earthworms • Arthropods = insects, crustaceans • Echinoderms = starfish • Chordates = humans, birds, fish, amphibians Slide 23 of 23