Lecture 22 Survey of Animals Invertebrates - 1

1. Lecture 22 Survey of Animals Invertebrates - 1

2. Animals • multicellular • Cells lack cell wall • Cells organized into specialized tissues • Heterotrophs • carbohydrate reserves as glycogen • Motile – at some point in life • some sessile for part or most of life • Sexual reproduction – diploid dominant form (asexual by budding in some) • Develop via blastula

3. Animal Classification/Evolution • Degree and type of tissue/organ development • Body plan • Tissue/cell layers • Symmetry – bilateral/radial • Presence/type of body cavity: • Presence/absence of dorsal nerve cord/notocord • Type of embryological Development

5. Invertebrates • Animals that lack backbone • Distributed amongst 9 phylla Chordates – Phylum Chordata • Animals with dorsal notochord + dorsal nerve chord • A few forms lack a backbone and are therefore invertebrates • All vertebrates are chordates • Not all chordates are …

6. Symmetry: • Asymmetrical: None • Example: Sponges • Radial • Body parts arranged in repeating units around a central axis – like a pie • Example: starfish • Sessile or slow moving • Food comes to animal • Bilateral • Split lengthwise results in mirror image sections • Example: lobster, cat, human • Active search for food • Cephalization: Sensory nerves at front

7. Body Cavities - Acoelomate Gut cavity but no other cavity epidermis gut cavity no body cavity; region between gut and body wall packed with organs Figure 25.4aPage 417

8. Body Cavities - Pseudocoel Gut Cavity + Body Cavity Psuedo = not “real” since it has no cells lining epidermis gut cavity unlined body cavity (pseudocoel) around gut Figure 25.4bPage 417

9. Body Cavities - Coelom Gut & “real” body cavity Real Coelom since it is lined with cells gut cavity peritoneum lined body cavity (coelom) Figure 25.4cPage 417

10. Porifera (Sponges) - Parazoa • symmetry – none - assymetric • How many cell layers are present? • 2 cell layers • What kind of cell specializations? • Choanocytes (= collar cells) • Epithelial cells • amoebocytes • Do you find specialized tissues in these animals? • No • Where are they found? • Mostly marine (salt water) but some in freshwater • Sessile: Anchored to sea floor – rocks, etc. • Filter feeders • Reproduce sexually • Microscopic swimming larval stage

12. Filter feeders: Water is pulled through pores in the body, and food is filtered out; rest of the water exits from the opening.

14. Choanocytes: closely resemble choanoflagellates (a protist) • Possible ancestor of all animals Choanocytes

15. Hydra Corals Seaanemone Jellyfish Tissues and Organization - Eumetazoans • Cnidaria and Ctenophora (Radiata) • 10,000 species mostly marine

17. Cnidarians • Carnivores that capture their prey with tentacles • Bear unique stinging cells called cnidocytes • Contain a small but powerful harpoon called a nematocyst • Only animals that produce nematocysts • Nerve net • Hydrostatic skeleton • Saclike gut • A major evolutionary innovation among the radiates is extracellular digestionof food • In radiates, digestion begins in the gastrovascular cavity

18. Radita: (Corals, sea anemones, jellyfish, Hydra – zooplankton) • What kind of symmetry do they exhibit? • radial • Where would you expect to find these creatures? • Aquatic habitats, as adults they are sessile • How many cell layers/tissues are present? • 2, endoderm and ectoderm • What kind of cell specializations? • Nerve/sensory, cnidocytes, glandular cells secrete digestive enzymes, contractile cells

20. The structure of eumetazoans is much more complex than that of sponges Radially symmetric eumetazoans form two distinct embryonic layers An outer ectoderm epidermis An inner endoderm gastrodermis A jelly-like layer called the mesoglea forms between the epidermis and gastrodermis Cnidarians: Tissues Lead to Greater Specialization

21. Medusae • Free-floating, release gametes – cross fertilization • Polyps • Cylindrical, pipe-shaped and usually attached to a rock • Cnidarians have two basic body forms • Cnidarians may exist exclusively as either/or • Others alternate between the two phases

23. Scyphozoans • Jellyfish • Anthozoans • Sea anemones • Corals • Hydrozoans

24. Bilateral Symmetry • Right and left half • Anterior: Head and Posterior: tail • Cephalization: concentration of nervous tissues/sensory in anterior end • Dorsal (back) and ventral (bottom) surfaces

25. Phylum Platyhelminthes: • 20,000 species • Acoelomate, bilateral, cephalized animals • All have simple or complex organ systems • Most are hermaphrodites • Tissue layers: • Ectoderm • Mesoderm • Endoderm Nervous system +

26. Planaria Platyhelminthes • The largest phylum of solid worms • Simplest animals in which organs occur • Include free-living and parasitic forms • Turbellarians (Turbellaria) • Flukes (Trematoda) • Tapeworms (Cestoda)

28. Life cycle of the human liver fluke, Clonorchis sinensis

29. Flatworms • Have incomplete gut with only one opening • Cannot eat, digest and excrete food simultaneously • Have an excretory system consisting of a network of tubules running throughout the body • Have a simple nervous system • Lack a circulatory system • Most are hermaphroditic

30. http://www.pbs.org/kcet/shapeoflife/animals/