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Animal Development and Phylogeny: Germ Layers, Coelom Formation, and Symmetry

This article explores the development and phylogeny of animals, focusing on topics such as germ layers, coelom formation, and symmetry. It provides an overview of different animal groups and their evolutionary relationships.

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Animal Development and Phylogeny: Germ Layers, Coelom Formation, and Symmetry

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  1. Fig. 32-1

  2. Fig. 32-2-3 Blastocoel Endoderm Cleavage Cleavage Blastula Ectoderm Archenteron Eight-cell stage Zygote Gastrulation Gastrula Blastocoel Blastopore Cross section of blastula

  3. Individual choanoflagellate Fig. 32-3 Choanoflagellates OTHER EUKARYOTES Sponges Animals Collar cell (choanocyte) Other animals

  4. Fig. 32-7 (a) Radial symmetry (b) Bilateral symmetry

  5. Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) (a) Coelomate Fig. 32-8 Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate

  6. Deuterostome development (examples: echinoderm, chordates) Protostome development (examples: molluscs, annelids) (a) Cleavage Eight-cell stage Eight-cell stage Radial and indeterminate Spiral and determinate Fig. 32-9 (b) Coelom formation Key Coelom Ectoderm Mesoderm Archenteron Endoderm Coelom Blastopore Mesoderm Mesoderm Blastopore Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. (c) Fate of the blastopore Anus Mouth Digestive tube Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

  7. “Porifera” Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Fig. 32-10 Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Rotifera Protostomia Mollusca Annelida Arthropoda Nematoda

  8. Silicea “Porifera” Calcarea ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Cnidaria Eumetazoa Acoela Fig. 32-11 Echinodermata Deuterostomia Chordata Bilateria Platyhelminthes Rotifera Ectoprocta Lophotrochozoa Brachiopoda Mollusca Annelida Nematoda Ecdysozoa Arthropoda

  9. Common ancestor of all animals Sponges (basal animals) Metazoa Ctenophora Fig. 32-UN1 Eumetazoa Cnidaria True tissues Acoela (basal bilaterians) Deuterostomia Bilateria (most animals) Bilateral summetry Lophotrochozoa Three germ layers Ecdysozoa

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