Introduction to Invertebrates

1. Introduction to Invertebrates Chapter 29 Mader: Biology 8th Ed.

2. Outline • Evolution of Animals • Sponges • Cnidarians and Comb Jellies • Hydra • Obelia • Bilateral Symmetry • Flatworms • Roundworms Mader: Biology 8th Ed.

3. Evolution of Animals • All animals are multicellular heterotrophic organisms that must take in preformed food. • Classification Criteria • Level of organization • Cellular, tissue, organ • Body Plan • Sac, tube-within-a-tube • Segmentation • Segmentation leads to specialization. Mader: Biology 8th Ed.

4. Evolution of Animals • Symmetry • Radial - Two identical halves. • Bilateral - Definite right and left halves. • Type of Coelom • Pseudocoelom • Coelom • Protostome - First embryonic opening becomes the mouth. • Dueterostome - Second embryonic opening becomes the mouth. Mader: Biology 8th Ed.

5. Multicellularity • Sponges • Only level of animal to have cellular organization. • Saclike bodies perforated by many pores. • Beating of flagella produces water currents that flow through pores into central cavity and out osculum. • Sessile filter feeders. • Asexual reproduction by fragmentation or budding. Mader: Biology 8th Ed.

6. Simple Sponge Anatomy Mader: Biology 8th Ed.

7. True Tissue Layers • Total of three possible germ layers. • Ectoderm, endoderm, and mesoderm • Animals in phlyum Ctenophora (comb jellies) and in phylum Cnidaria (cnidarians) develop only ectoderm and endoderm. • Diploblasts • Radially symmetrical Mader: Biology 8th Ed.

8. Cnidarian and Comb Jelly Mader: Biology 8th Ed.

9. Comb Jellies • Small, transparent, and often luminescent. • Most of body composed of mesoglea. • Largest animals propelled by beating of cilia. • Capture prey with tentacles. Mader: Biology 8th Ed.

10. Cnidarians • Tubular animals that most often reside in shallow marine waters. • Polyp and medusa body forms. • Specialized stinging cells (cnidocytes). • Fluid-filled capsule, nematocyst. • Two-layered body sac. • Outer layer - Protective epidermis. • Inner layer - Gastrovascular cavity. • Nerve net found throughout body. Mader: Biology 8th Ed.

11. Cnidarian Diversity Mader: Biology 8th Ed.

12. Hydra • Freshwater cnidarians. • Small tubular poly body about one-quarter inch in length. • Gastrovascular cavity is central cavity. • Tentacles can respond to stimuli. • Can reproduce sexually and asexually. Mader: Biology 8th Ed.

13. Hydra Mader: Biology 8th Ed.

14. Obelia • A colony of polyps enclosed by a hard, chitinous covering. • Feeding polyps • Extend beyond covering • Have nematocyst-bearing tentacles. • Reproductive polyps • Budding of new polyps. • Also has sexual reproduction (medusae) stage. Mader: Biology 8th Ed.

15. Obelia Mader: Biology 8th Ed.

16. Bilateral Symmetry • Ribbon worms (phylum Nemertea) • Have distinctive proboscis • Flatworms (phylum Platyhelminthes) • Majority are parasitic • Organ-level organization • No specialized circulatory or respiratory structures. • Have undergone cephalization • Ladder-type nervous system Mader: Biology 8th Ed.

17. Free-living Flatworms • Planarians (genus Dugesia) • Live in freshwater habitats. • Head is bluntly arrow shaped. • Auricles function as sense organs. • Two light-sensitive eye spots. • Three kinds of muscle layers: • Outer circular layer • Inner longitudinal layer • Diagonal layer Mader: Biology 8th Ed.

18. Planarians • Excretory organ functions in osmotic regulation and water excretion. • Can reproduce asexually • Hermaphroditic • Practice cross-fertilization Mader: Biology 8th Ed.

19. Mader: Biology 8th Ed.

20. Parasitic Flatworms • Parasitic flatworms are flukes (trematodes) and tapeworms (cestodes). • Well-developed nerves and gastrovascular cavity are unnecessary. • Flukes • Usually named for type of vertebrate organ they inhabit. • Reproductive system well developed. • Usually hermaphroditic. Mader: Biology 8th Ed.

21. Transmission of Schistosomiasis Mader: Biology 8th Ed.

22. Parasitic Flatworms • Tapeworms • Have anterior region with modifications for attachment to intestinal wall of host. • Behind head region, scolex, a long series of proglottids are found. • Segments each containing a full set of both male and female sex organs. • Complicated life cycles. Mader: Biology 8th Ed.

23. Life Cycle of Taenia Mader: Biology 8th Ed.

24. Pseudocoelom • Pseudocoelom is a false body cavity that is incompletely lined by mesoderm. • Provides a space for internal organs and can serve as hydrostatic skeleton. • Roundworms (phylum Nematoda) • Nonsegmented, generally colorless worms. • Several parasitic roundworms infect humans. Mader: Biology 8th Ed.

25. Roundworm Anatomy Mader: Biology 8th Ed.

26. Parasitic Roundworms • Ascaris • Trachinella - Trichinosis • Dirofilaria - Heartworms • Wuchereria - Elephantiasis Mader: Biology 8th Ed.

27. Rotifers • Rotifers (phylum Rotifera) • Named for crown of cilia resembling a rotating wheel. • Serves as both as an organ of locomotion and aids direction of food to mouth. Mader: Biology 8th Ed.

28. Rotifer Mader: Biology 8th Ed.

29. Review • Evolution of Animals • Sponges • Cnidarians and Comb Jellies • Hydra • Obelia • Bilateral Symmetry • Flatworms • Roundworms Mader: Biology 8th Ed.

30. Mader: Biology 8th Ed.