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Introduction to Animal Evolution

Introduction to Animal Evolution. Fred Searcy, Jr. Broward Community College. Metazoans. Includes 22 phyla, including Chordates Multicellular creatures Significantly different from unicellular and colonial protozoans. Protozoa vs. Metazoa. Unicellular Multicellular

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Introduction to Animal Evolution

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  1. Introduction to Animal Evolution Fred Searcy, Jr. Broward Community College

  2. Metazoans • Includes 22 phyla, including Chordates • Multicellular creatures • Significantly different from unicellular and colonial protozoans

  3. Protozoa vs. Metazoa UnicellularMulticellular little or no relationships specialization of between cells cells to form tissues, organs, systems motile, few sessile motile & sessile autotrophic & heterotrophic heterotrophic single sex cells, no embryo sex cells multicellular, embryo formed

  4. Symmetry in Metazoans • Radial • more adaptive to sessile organisms for feeding • Bilateral • allows head-tail organization and thus locomotion • more suited to free-swimming organisms

  5. Metamerism • Segmentation in bilateral organisms has arisen two separate places in the animal kingdom • annelid worms • chordates

  6. Body Cavities in Metazoans • Fluid-filled cavity between body wall and internal organs • Functions: • hydrostatic skeleton • circulatory medium • space to accumulate excess fluids • site for maturation of sperm and/or eggs • increases surface area of organs

  7. Body Cavities continued • Some have no body cavity; instead filled with an aggregation of cells called mesenchyme • Two cavity types • pseudocoelomate (from a persistent blastocoel) • coelomate (formed from mesoderm while in embryo) • Mesoderm forms lining for all internal organs called the peritoneum • Where it supports organs, called mesentery

  8. Metazoan Organ Systems • Differentiation of cells to from tissues, organs, and systems • example is excretion • filtration • secretion • selective reabsorption

  9. Metazoan Embryology • Metazoans divided into two major groups based on embryology • Protostomia • Deuterostomia • Based on • egg types • determinate vs. indeterminate cleavage • spiral vs radial cleavage • mesoderm and coelom formation

  10. Egg Types • There are three types of eggs based on yolk distribution isolecithal centrolecithal telolecithal

  11. Determinate vs Indeterminate Cleavage • As zygote undergoes mitosis, goes from single cell, to 2, 4, 8, 16, 32, 64, etc. • At what time does a cell cease being an entity and become specialized, i.e. blood cell? • Embryonic fate determined late in deuterostomes, early in protostomes • break a 4-cell stage of starfish apart, get 4 identical starfish • break 4-cell stage apart in flatworm, get 4 quarters of an animal

  12. Spiral vs Radial Cleavage • Deuterostomes undergo radial cleavage • blastopore become anus • Protostomes undergo spiral cleavage • blastopore becomes mouth

  13. Embryology in an Isolecithal Egg 2-cell stage Unfertilized egg Fertilized egg 4-cell stage 16-cell stage Morula (32) Morula (64) blastocoel 8-cell stage blastocoel invagination Archenteron & blastopore Early gastrulation

  14. Embryology in A Telolecithal Egg Epiboly & involution

  15. Embryology in A Telolecithal Egg

  16. Mesoderm and Coelom Origin • Protostomes - mesoderm arises from a single cell • mesodermic masses form and split to form a pocket • called schizocoely • Deuterostomes - meoderm formed from puckering of endodermal tissue • called enterocoelic pouching

  17. Schizocoely

  18. Schizocoely continued

  19. Schizocoely

  20. Enterocoely

  21. Enterocoely

  22. Body Cavity Forms • Acoelomate - no body cavity

  23. Body Cavity Forms • Pseudocoelomate - from a persistent blastocoel

  24. Body Cavity Forms • Coelomate - true body cavity

  25. Synopsis of Metazoan Phyla • Parazoa - metazoans with poorly defined tissues, no organs present [Phylum Porifera (10,000) Sponges] • Eumetozoa - metazoans with organs, mouth, digestive cavity • Radiates • Phylum Cnidaria (8,900) jellyfish, anemones, corals • Phylum Ctenophora (90) comb jellies • Bilateria

  26. Synopsis continued • Bilateria • Acoelomates • Phylum Platyhelminthes (12,700) flatworms, flukes • Phylum Mesozoa (50) marine parasites • Phylum Rhyncocoela (650) nemerteans • Phylum Gnathostomulida (80) acoeolmate worms • Pseudocoelomates • Phylum Rotifera (1,500) rotifers • Phylum Gastrotricha (400) gastrotrichs • Phylum Nematoda (10,000) roundworms

  27. Synopsis continued • Pseudocoelomates continued • Phylum Nematomorpha (230) hairworms • Phylum Acanthocelphala (500) endoparasites • Schizocoelomates • Phylum Priapulida (8) • Phylum Sipunculida (250) marine worms • Phylum Mollusca (80,000) mussels, clams • Phylum Echiurida (60) • Phylum Annelida (8,700) segmented worms • Phylum Pogonophora (80) • Phylum Tardigrada (180) water bears

  28. Synopsis continued • Schizocoelomates continued • Phylum Onychophora (65) • Phylum Arthropoda (923,000) insects, crayfish • Phylum Pentastomida (70) • Phylum Phoronida (15) • Phylum Bryozoa (4,000) • Phylum Entoprocta (60) • Phylum Branchiopoda (260) • Deuterostomes • Phylum Chaetognatha (50) • Phylum Echinodermata (5,300) starfish

  29. Synopsis continued • Deuterostomes • Phylum Hemichordata (80) • Phylum Chordata (39,000) • Phylum Urochordata (1,600)

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