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Animals

This article explores the fascinating world of animal evolution, covering key characteristics that define animals, such as being multicellular, heterotrophic eukaryotes without cell walls. It delves into the stages of animal development from zygote to gastrula, discusses various organizational levels from cellular to tissue, and examines body symmetry and cavities. Additionally, the differences between protostomes and deuterostomes are outlined, shedding light on their development and segmentation. With insights into animal phylogeny, this resource highlights the common ancestry of all animals.

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Animals

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  1. Animals Introduction to Animal Evolution

  2. What is an Animal? • Multicellular, heterotrophic, eukaryotes • Cells lack cell walls, held together by structural proteins (collagen) • Contain nervous and muscle tissue • Most reproduce sexually with a dominant diploid stage

  3. Development • Zygote (cleavage) • Morula • Blastula • Gastrula • Blastopore • Archenteron • Two layers of tissue (endoderm & ectoderm)

  4. Origin of Animals

  5. Animal Phylogeny

  6. Animal Phylogeny

  7. Animal Phylogeny Overview • Organization Level • Body Symmetry • Body Cavities • Development • Segmentation

  8. Organization Level • Cellular Level vs. Tissue Level • Cellular Level: Porifera (sponges) • Tissue Level: all others

  9. Body Symmetry • Radial vs. Bilateral • Radial Symmetry: Cnidaria & Ctenophora • Bilateral Symmetry: all others

  10. Body Cavities • Acoelomates: Platyhelminthes (flatworms) • Pseudocoelomates: Nematoda (roundworms) • Eucoelomates: all others

  11. Development • Protostomes vs. Deuterostomes

  12. Cleavage Spiral and Determinate Coelom Formation Schizocoelous Formed from 4D cells Fate of Blastopore Mouth Cleavage Radial and Indeterminate Coelom Formation Enterocoelous Formed from pockets of the archenteron Fate of Blastopore Anus Protostomes vs. Deuterostomes

  13. Development • Protostomes vs. Deuterostomes • Protostomes: • Mollusca (clams, snails) • Annelida (segmented worms) • Arthropoda (Crustaceans, insects) • Deuterostomes • Echinodermata (Seastars) • Chordata (vertebrates)

  14. Segmentation • Mollusca (soft - unsegmented) • Annelida (soft – segmented) • Arthropoda (hard – segmented) • Chordata (segmented)

  15. Which Phylogeny?

  16. Points of agreement • 1. All animals have common ancestor • 2. Sponges are basal animals • 3. All other animals have true tissues • 4. Most animals are bilateral • 5. Chordates and Echinoderms are related (deuterostomes)

  17. Points under Contention • Animals not in the clade deuterostomes are divided into two groups: • Ecdysozoans • Lophotrochozoans

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