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Exploring Evolution of Invertebrates: A Comprehensive Overview

Dive into the evolutionary journey of invertebrates, from sponges and true tissues to cnidarians and flatworms. Learn about multicellularity, body cavities, and symmetry in this fascinating exploration.

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Exploring Evolution of Invertebrates: A Comprehensive Overview

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  1. Introduction to Invertebrates

  2. Outline • Evolution of Animals • Multicellularity • Sponges • True Tissues • Cnidarians and Comb Jellies • Hydra • Obelia • Bilateral Symmetry • Flatworms • Roundworms • Body Cavities • Acoelomates • Psuedocoelomates • Eucoelomates

  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

  4. Evolution of Animals • Classification Criteria, cont • Symmetry • Radial - Two identical halves • Bilateral - Definite right and left halves • Type of Coelom • Pseudocoelom • Coelom • Early Developmental Pattern • Protostome - First embryonic opening becomes the mouth • Dueterostome - Second embryonic opening becomes the mouth

  5. Animals:Multicellular, Heterotrophic Eukaryotes

  6. Traditional Phylogenetic Tree of Animals

  7. 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

  8. Simple Sponge Anatomy

  9. True Tissue Layers • Total of three possible germ layers • Ectoderm • Endoderm, and • Mesoderm • phlya Ctenophora and Cnidaria develop only ectoderm and endoderm • Diploblasts • Radially symmetrical

  10. Comb Jellies • Small, transparent, and often luminescent • Most of body composed of mesoglea • Largest animals propelled by beating of cilia • Capture prey with tentacles

  11. Comb Jelly Compared to Cnidarian

  12. 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

  13. Cnidarian Diversity

  14. Hydra • Freshwater cnidarian • 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

  15. Anatomy of Hydra

  16. 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

  17. Obelia Life Cycle

  18. 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

  19. Ribbon Worm, Lineus

  20. 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

  21. Planarian Anatomy

  22. Planarians • Planarians, cont. • Excretory organ functions in osmotic regulation and water excretion • Can reproduce asexually • Hermaphroditic • Practice cross-fertilization

  23. Parasitic Flatworms • Parasitic flatworms are flukes (trematodes) and tapeworms (cestodes) • Well-developed nerves and gastrovascular cavity are unnecessary • Flukes • Reproductive system well developed • Usually hermaphroditic

  24. Life Cycle of Schistosomiasis

  25. 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

  26. Life Cycle of a Tapeworm, Taenia

  27. Pseudocoelom • Pseudocoelom: • 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) • Non-segmented, generally colorless worms • Several parasitic roundworms infect humans

  28. Roundworm Anatomy

  29. Parasitic Roundworms • Ascaris – Intestinal roundworm • Trachinella - Trichinosis • Dirofilaria - Heartworms • Wuchereria - Elephantiasis

  30. Filarial Worm

  31. 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

  32. Rotifer

  33. Review • Evolution of Animals • Multicellularity • Sponges • True Tissues • Cnidarians and Comb Jellies • Hydra • Obelia • Bilateral Symmetry • Flatworms • Roundworms • Body Cavities • Acoelomates • Psuedocoelomates • Eucoelomates

  34. Introduction to Invertebrates

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