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Exploring Animal Evolution: From Unicellular Ancestor to Diverse Forms

Delve into the fascinating world of animal evolution, from their unique characteristics like lack of cell walls to the role of regulatory genes like Hox genes. Explore the phylogeny and diversity of animals, including the Parazoa-Eumetazoa and Radiata-Bilateria dichotomies. Understand the significance of germ layer development and the grades of Acoelomate, Pseudocoelomate, and Coelomate animals. Discover the Protostome-Deuterostome dichotomy and how it shapes the evolution of coelomates. Join this journey through the evolution of animals and gain a deeper understanding of their origins and development.

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Exploring Animal Evolution: From Unicellular Ancestor to Diverse Forms

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  1. Chapter 32 • Introduction to Animal Evolution

  2. Def: an•i•mal (n) Unique characteristics: • Heterotrophic eukaryotes; ingestion • Lack cell walls; collagen • Nervous & muscular tissue • Sexual; diploid; cleavage; blastula; gastrulation; larvae; metamorphosis • Regulatory genes: Hox genes

  3. Animal phylogeny & diversity, I • Monophyletic; colonial flagellated protist ancestor • 1- Parazoa-Eumetazoa dichotomy: sponges (Parazoa)~ no true tissues; all other animals (Eumetazoa)~ true tissues • 2- Radiata-Bilateria dichotomy: Cnidaria (hydra; ‘jellyfish’; sea anemones) & Ctenophora (comb jellies)~ radial body symmetry; all other animals~ bilateral body symmetry (also: cephalization)

  4. Animal phylogeny & diversity, II • 3- Gastrulation: germ layer development; ectoderm (outer), mesoderm (middle), endoderm (inner); radiata are diploblastic-2 layers; no mesoderm; bilateria are triploblastic-all 3 layers • 4- Acoelomate, Pseudocoelomate, and Coelomate Grades: triploblastic animals~ solid body, no body cavity called acoelomates (Platyhelminthes-flatworms); body cavity, but not lined with mesoderm called pseudocoelomates (Rotifers); true coelom (body cavity) lined with mesoderm called coelomate

  5. Animal phylogeny & diversity, III • 5- Protostome-Deuterostome dichotomy among coelomates: protostomes (mollusks, annelids, arthropods); deuterostomes (echinoderms, chordates) • a) cleavage: protostomes~ spiral and determinate; deuterotomes~ radial and indeterminate • b) coelom formation: protostomes~ schizocoelous; deuterostomes~ enterocoelous • c) blastopore fate: protostomes~ mouth from blastopore; deuterostomes~ anus from blastopore

  6. NOVA • https://www.youtube.com/watch?v=ujYNSDYIZKw

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