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Animal Evolution –The Invertebrates

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  1. Animal Evolution –The Invertebrates Chapter 25 Part 1

  2. Impacts, IssuesOld Genes, New Drugs • Humans and other vertebrates share genes with invertebrates, including the cone snail – which makes powerful conotoxins

  3. 25.1 Animal Traits and Body Plans • Animals • Multicelled heterotrophs that move about during part or all of the life cycle • Body cells do not have a wall and are typically diploid • The overwhelming majority are invertebrates

  4. Animal Body Plans: Organization • Tissues • Cells of a particular type and function, organized in a specific pattern • Tissue formation begins in an embryo • Ectoderm and endoderm • Mesoderm

  5. Tissue Formation • Formation of a three-layer animal embryo

  6. ectoderm mesoderm endoderm Fig. 25-2, p. 404

  7. Animal Body Plans: Body Symmetry • Body Symmetry • Simplest animals are asymmetrical (sponges) • Jellyfish and hydras have radial symmetry • Most animals have bilateral symmetry • Cephalization • In most bilateral animals, nerve cells are concentrated at the head end

  8. Body Symmetry

  9. posterior anterior Fig. 25-3, p. 405

  10. Animal Body Plans: Gut and Body Cavity • Gut • Digestive sac (incomplete digestive system) or tube (complete) that opens at the body surface • Typically, a body cavity surrounds the gut • Coelom: Cavity lined by mesodermal tissue • Pseudocoel: Cavity is partially lined • Acoelomates have no body cavity

  11. Body Cavities

  12. Fig. 25-4a, p. 405

  13. epidermis gut cavity organs packed between gut and body wall A No coelom (acoelomate animal) Fig. 25-4a, p. 405

  14. Fig. 25-4b, p. 405

  15. epidermis gut cavity B Pseudocoel (pseudocoelomate animal) unlined body cavity around gut Fig. 25-4b, p. 405

  16. Fig. 25-4c, p. 405

  17. gut cavity epidermis C Coelom (coelomate animal) body cavity with a lining (dark blue) derived from mesoderm Fig. 25-4c, p. 405

  18. Animation: Types of body cavities

  19. Two Lineages of Bilateral Animals • Protostomes • First opening in the embryo becomes the mouth • Second opening becomes the anus • Deuterostomes • First opening in the embryo becomes the anus • Second opening becomes the mouth

  20. Animal Body Plans: Circulation • In small animals, gases and nutrients diffuse through the body • Most animals have a circulatory system • Closed circulatory system: Heart pumps blood through a continuous vessel system • Open circulatory system: Blood leaves the vessels

  21. Animal Body Plans: Segmentation • Many bilateral animals are segmented • Similar units repeated along length of body • Repetition allows evolution of specialization

  22. Variation in Animal Body Plans

  23. 25.2 Animal Origins and Adaptive Radiation • Fossils and gene comparisons among modern species provide insights into how animals arose and diversified

  24. Becoming Multicellular • Animals probably evolved from a colonial, choanoflagellate-like protist • Choanoflagellates (“collared flagellate”) • Modern protists most closely related to animals • A collar of microvilli surrounds the flagellum • Have proteins similar to adhesion or intercellular signaling proteins in animals

  25. Choanoflagellates

  26. Fig. 25-5a, p. 406

  27. Fig. 25-5b, p. 406

  28. Fig. 25-5c, p. 406

  29. amoebozoans fungi choanoflagellates animals Fig. 25-5c, p. 406

  30. A Great Adaptive Radiation • Animals underwent a dramatic adaptive radiation during the Cambrian

  31. Relationships and Classification • Animals have traditionally been classified based on morphology and developmental pattern • Mainly features of body cavities • A newer system puts all animals with a three-layer embryo into protostomes or deuterostomes • Protostomes are divided into animals that molt (Ecdysozoa) and don’t molt (Lophotrochozoa)

  32. Relationships and Classification

  33. Relationships and Classification

  34. chordates Deuterostomes echinoderms arthropods tardigrades Protostomes annelids mollusks Coelomate animals rotifers Pseudocoelomate animals roundworms flatworms Acoelomate animals Animals with a 3-layer embryo cnidarians Animals with tissues sponges Animals placozoans Fig. 25-7a, p. 407

  35. Deuterostomes chordates echinoderms arthropods Ecdysozoa tardigrades roundworms Protostomes rotifers mollusks Lophotrochozoa annelids flatworms Animals with a 3-layer embryo cnidarians Animals with tissues sponges placozoans Animals Fig. 25-7b, p. 407

  36. 25.1-25.2 Key ConceptsIntroducing the Animals • Animals are multicelled heterotrophs that actively move about during all or part of the life cycle • Early animals were small and structurally simple • Their descendants evolved a more complex structure and greater integration among specialized parts

  37. 25.3 The Simplest Living Animal • Placozoans, the simplest known animals, have no body symmetry, no tissues, and just four different types of cells • Example: Trichoplax adherens

  38. 25.4 The Sponges • Sponges are simple but successful; they have survived in seas since Precambrian times • Sponges (phylum Porifera) • Attach to seafloor or other surfaces • No symmetry, tissues, or organs • Pores with flagellated collar cells filter water • Sexual or asexual reproduction

  39. Sponges

  40. Fig. 25-9a, p. 409

  41. Fig. 25-9b, p. 409

  42. Fig. 25-9c, p. 409

  43. Fig. 25-9d, p. 409

  44. Sponge Body Plan

  45. water out glassy structural elements amoeboid cell pore semifluid matrix central cavity flattened surface cells collar cell water in water in flagellum collar of microvilli nucleus Fig. 25-10, p. 409

  46. Sponge Reproduction and Dispersal • Hermaphrodite • Individual that produces both eggs and sperm • Sperm are released into water; eggs are retained • Zygote develops into ciliated larva • Larva • Free-living, sexually immature stage in life cycle • Settles and develops into adult

  47. Sponge Characteristics • Toxins and fibrous or sharp body parts deter predators • Some freshwater sponges survive unfavorable conditions by producing gemmules • Sponges show cell adhesion, self-recognition

  48. 25.5 Cnidarians—True Tissues • Cnidarians (phylum Cnidaria) • Radial animals with two tissue layers • Medusae (jellyfishes) are bell shaped and drift • Polyps (sea anemones) are tubular with one end usually attached to a surface • Four classes: hydrozoans, anthozoans, cubozoans, and scyphozoans

  49. Two Cnidarian Body Plans

  50. gastrovascular cavity outer epithelium (epidermis) mesoglea (matrix) inner epithelium (gastrodermis) gastrovascular cavity Fig. 25-11, p. 410