CHAPTER 9

1. CHAPTER 9 Architectural Pattern of an Animal 9-1

2. New Designs for Living • Zoologists recognize 34 major phyla of living multicellular animals • Survivors of around 100 phyla that appeared 600 million years ago during Cambrian explosion • Most important evolutionary event in geological history of life • Virtually all major body plans evolved • Major body plans • Result of extensive selection • Are limiting determinant of future adaptational variants

3. Grades of Organization: Unicellular Multicellular Tissue Tissue-Organ Organ System

4. Table 9.1

5. Hierarchical Organization of Animal Complexity • Grades of Organization • Unicellular protozoans • Simplest eukaryotic organisms • Protoplasmic Grade of Organization • Perform all basic functions with confines of single cell

6. Hierarchical Organization of Animal Complexity • Metazoa • Multicellular animals • Cells are specialized parts of whole organism • Cannot live alone • Cellular Grade of Organization • Simplest metazoans • Cells demonstrate division of labor but are not strongly associated to perform a specific collectivefunction

7. Hierarchical Organization of Animal Complexity • Tissue Grade of Organization • Cells grouped together • Perform common function as a unit (tissue) • Tissue-Organ Grade of Organization (Eumetazoans) • Tissues assembled into larger functional units called organs • Chief functional cells of an organ- Parenchyma • Supportive tissues of an organ- Stroma

8. Hierarchical Organization of Animal Complexity • Organ-System Grade of Organization • Organs work together to perform a common function • Highest level of organization • Associated with most animal phyla

9. Symmetry

11. Animal Body Plans • Animal Symmetry • Symmetry • Correspondence of size and shape of parts on opposite sides of a median plane (a vertical plane that divides an organism into symmetrical halves.) Spherical symmetry • Any plane passing through center divides body into mirrored halves • Best suited for floating and rolling • Found among some unicellular forms • Rare in animals

12. 1. Spherical symmetry • Any plane passing through center divides body into mirrored halves • Best suited for floating and rolling • Found among some unicellular forms • Rare in animals

13. Animal Body Plans 2. Radial symmetry • Body divided into similar halves by more than 2 planes passing through longitudinal axis a. Biradial symmetry • Variant form radial symmetry • Have part that is single or paired rather than radial • Only 2 planes passing through longitudinal axis produces mirrored halves • Usually sessile, freely floating, or weakly swimming animals • No anterior or posterior end • Can interact with environment in all directions

15. Animal Body Plans 3. Bilateral Symmetry • Organism can be divided along a sagittal plane into two mirror portions • Right and left halves • Much better fitted for directional (forward) movement • Associated with cephalization • Differentiation of a head region with concentration of nervous tissue and sense organs • Advantageous to an animal moving through its environment head first • Always accompanied by differentiation along an anteroposterior axis

17. Animal Body Plans • Regions of bilaterally symmetrical animals • Anterior • Head end • Posterior • Tail end • Dorsal • Back or upper side • Ventral • Front or belly side • Medial • Midline of body • Lateral • Sides

18. Animal Body Plans • Distal • Parts farther from the middle of body • Proximal • Parts are nearer the middle of body

19. Frontal plane (coronal plane) • Divides bilateral body into dorsal and ventral halves • Sagittal plane • Divides body into right and left pieces • Transverse plane (cross section) • Divides body into anterior and posterior portions

21. Fig. 9.3

22. Body Cavity

23. Body Cavities and Germ Layers • Body cavity • Sponges • Acoelomate: no body cavity • In sponges • After blastula formation, cells reorganize to form adult body • Blastula has no external opening • No gut forms

25. Body Cavities and Germ Layers • Other animal phyla • Development proceeds from blastula to gastrula • Blastula is a mass of cells that has undergone numerous cleavages after the zygote • Gastrula is what forms after the blastula when invagination begins to form • Invagination of surface cells form the archenteron or primitive gut • Opening to archenteron is the blastocoel • Becomes the mouth or the anus • Gut is lined by endoderm • Outer layer of cells is ectoderm

27. Body Cavities and Germ Layers Embryo now has 2 cavities • Gut and blastocoel • Blastocoelpersists in some animals • In others, becomes filled with a 3rd germ layer, mesoderm • Cells forming mesoderm • Derived from endoderm • 2 mechanisms of formation

29. The majority of coelomate invertebrates develop as protostomes ("first mouth") in which the oral end of the animal develops from the first developmental opening, the blastopore. In the deuterostomes("second mouth": cf. Deuteronomy, "second book of the law"), including Echinodermata and the ancestors of the Chordata, the oral end of the animal develops from a second opening on the dorsal surface of the animal; the blastopore becomes the anus.

30. ProtosomesvsDeuterostomes

33. Protosomes

34. Body Cavities and Germ Layers • In Protostomes • Mesoderm forms as endodermal cells near blastopore migrate into the blastocoel • Three body plans are possible • Acoelomate plan • Mesodermal cells completely fill the blastocoel • Gut is only body cavity

35. Body Cavities and Germ Layers • Pseudocoelomate plan • Mesodermal cells line the outer edge of the blastocoel • 2 body cavities formed • Persistent blastocoel (pseudocoelom) and a gut cavity • Pseudocoelom is a false body cavity (only partially lined with mesoderm)

36. Body Cavities and Germ Layers • Schizocoelous plan • Mesodermal cells fill blastocoel • Mesoderm splits • The space is called a coelom • True body cavity (completely lined by mesoderm) • 2 body cavities formed • Gut and coelom

38. Deuterostomes

40. Body Cavities and Germ Layers • In Deuterostomes • Mesoderm forms by an enterocoelous plan • Cells from central gut lining form pouches • Pouches expand into blastocoel • Wall forms mesodermal ring • Pouches enclose a space, coleom • Pouches pinch off from gut lining • 2 body cavities form • Gut and coelom

41. Fig. 9.3b

43. Diploblasts and TriploblastsDeuterostomes

46. Developmental Origins in Triploblasts Body Plans • Triploblastic animals follow one of several major developmental pathways • Most common pathways are by spiral or radial cleavage • Radial cleavage • Typically accompanied by 3 traits • Blastopore becomes the anus and new opening becomes the mouth • Coelom formation is by enterocoely • Cleavage is regulative • Animals with these features called deuterostomes

47. Developmental Origins in Triploblasts Body Plans • Spiral cleavage • Produces embryos whose developmental pattern contrast with those of deuterostomes • Blastopore becomes the mouth • Cleavage is mosaic • Mesoderm forms from 4d cell • May be acoelomate, pseudocoelomate, or coelomate (schizocoely) • Animals with these features are called lophotrochozoan protostomes

48. Developmental Origins in Triploblasts Body Plans • Ecdysozoanprotostomes • Exhibit a range of cleavage patterns including spiral cleavage • Coelomate or psuedocoelomate • Few diploblasts and triploblasts form blind gut • Same opening for entrance of food and exit of wastes • Most form a complete gut • Allows for one-way flow of food from mouth to anus • Tube-within-a-tube design

49. A Complete Gut Design and Segmentation • Metamerism (Segmentation) • Serial repetition of similar body segments along longitudinal axis of body • Each segment is a metamere or somite • Permits greater body mobility and complexity of structure and function • Annelids, Arthropods, Chordates