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Noncoelomate Invertebrates

Noncoelomate Invertebrates. Chapter 32. Invertebrate Phylogeny. Two Approaches Traditional reconstructions are based on key aspects of body architecture. lumping phyla that share fundamental aspects of body plan New reconstructions employ molecular comparisons.

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Noncoelomate Invertebrates

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  1. Noncoelomate Invertebrates Chapter 32

  2. Invertebrate Phylogeny • Two Approaches • Traditional reconstructions are based on key aspects of body architecture. • lumping phyla that share fundamental aspects of body plan • New reconstructions employ molecular comparisons. • focus on differences in ribosomal RNA sequences

  3. Traditional Protostome Phylogeny

  4. Novel rRNA Protostome Phylogenies • Two major clades • Lophotrochozoans • flatworms • mollusks • annelids • Ecdysozoans • roundworms • arthropods

  5. rRNA Protostome Phylogeny

  6. Parazoa • Sponges (Porifera) • most lack symmetry • adults are sessile • little coordination among cells • three functional layers • choanocytes • mesohyl • outer epithelial layer • spicules

  7. Parazoa • Beating of flagella lining interior draws water in through numerous pores. • Small organisms are filtered out of the water, which flows through passageways and eventually out an osculum. • Reproduction done by fragmentation as well as sexually.

  8. Sponges

  9. Radiata • Distinct tissues • epidermis and nervous system develop from ectoderm • gastrodermis develops from endodermis • True body symmetry • Radiata • Cnidaria • Ctenophora • Bilateria • all others

  10. Radiata • Cnidarians • nearly all marine • carnivorous • cnidocytes • nematocysts • two basic body plans • polyps and medusae • fertilized eggs give rise to planulae • internal extracellular digestion

  11. Two Body Forms

  12. Cnidarians

  13. Radiata • Classes of Cnidarians • Hydrozoa - hydroids • Scyphozoa - jellyfish • Cubozoa - box jellyfish • Anthozoa - sea anemones and corals • Ctenophorans (comb jellies) • propel through the water by means of eight comb-like plates of fused cilia

  14. Bilateral Acoelomates • Bilateral symmetry • digestive tract is only internal cavity • Phylum Platyhelminthes: the flatworms • Flatworms are among the simplest bilaterally symmetrical animals, but they have a definite head at the anterior end, and do possess organs.

  15. The Bilateral Acoelomates • Flatworms • cannot feed, digest, and eliminate food simultaneously • absorb food directly through body walls • have excretory system • flame cells • most are hermaphroditic

  16. Flatworm Architecture

  17. The Bilateral Acoelomates • Class Turbellaria: turbellarians • only one of three classes are freeliving • Class Trematoda: flukes • life cycle liver fluke Clonorchis sinensis • miracidium - eggs (passed in feces) • rediae - elongated, nonciliated larvae • cercariae - tadpole-like larval stage • metacercariae - adult stage

  18. The Bilateral Acoelomates • Class Cestoda: tapeworms • hang on to inner walls of their hosts by specialized terminal attachment organs, and absorb food through their skins. • scolex - attachment organ • neck - unsegmented • proglottids - repetitive segments

  19. The Bilateral Acoelomates • Phylum Nemertea: ribbon worms • simplest animals that possess a complete digestive system • mouth and anus

  20. The Pseudocoelomates • Internal body cavity • pseudocoel serves as hydrostatic skeleton • gains rigidity from being filled with fluid under pressure • lack a defined circulatory system

  21. The Pseudocoelomates • Phylum Nematoda: roundworms • bilaterally symmetrical unsegmented worms • covered by flexible, thick cuticle • mouth equipped with stylets • food passes through mouth as result of sucking action of pharynx • lack flagella or cilia • reproduction is sexual • Trichinella regularly parasitize humans

  22. Roundworms

  23. Nematode-Caused Diseases • Trichinosis - Trichinella • Pinworms - Enterobius • Intestinal roundworms - Ascaris • Filariasis - Filaria

  24. The Pseudocoelomates • Phylum Rotifera: rotifers • small, bilaterally symmetrical, basically aquatic animals with a crown of thick cilia at their heads • well developed food processing apparatus • “wheel animals” • Phylum Cycliophora • relatively new • circular mouth surrounded by fine, hairlike cilia

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