CH 23 - Chapter 23 Animal Diversity I Invertebrates 23.1...

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Chapter 23 Animal Diversity I: Invertebrates
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23.1 What Are the Key Features of Animals? Animals possess all of the following characteristics 1. Multicellularity 2. Their cells lack a cell wall 3. They obtain energy by consuming other organisms 4. Most reproduce sexually 5. They are motile at some point in the life cycle 6. They are able to respond rapidly to external stimuli
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23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? Most animal phyla that currently populate Earth were present by the Cambrian (544 MYA) Few pre-Cambrian fossils led systematists to look for clues about the evolutionary history of animals using Anatomy Embryological development DNA sequences Certain features represent evolutionary milestones, with major branching points on the animal tree 1.The appearance of tissues 2.The appearance of body symmetry 3.Protostome and deuterostome development
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Ectoderm (top layer) Mesoderm (middle layer) Endoderm (bottom layer)
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An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1
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Lack of tissues separates sponges from all other animals Tissues are groups of similar cells that carry out a specific function (e.g., muscle) There are 3 types of tissue layers 1. Ectoderm 2. Mesoderm 3. Endoderm Sponges are the only modern-day animals lacking tissue Individual cells in sponges may be specialized, but they act independently and are not organized into true tissues Sponges and all remaining tissue-containing phyla arose from an ancient common ancestor without tissue
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Animals with tissues exhibit either radial or bilateral symmetry Symmetrical animals have an upper (dorsal) surface and a lower (ventral) surface Symmetrical animals are divided into two groups: Animals that exhibit radial symmetry Animals that exhibit bilateral symmetry
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Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis Animals with radial symmetry have two embryonic tissue (germ) layer Ectoderm , which is an outer layer that covers the body, lines its inner cavities, and forms the nervous system Endoderm , which is an inner layer that lines most hollow organs Bilaterally symmetrical animals have three embryonic tissue (germ) layers A layer of mesoderm between the ectoderm and endoderm forms muscles and the circulatiory and skeletal system
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Bilaterally symmetrical animals have heads Animals with bilateral symmetry can be divided into mirror-image halves only along one plane that runs down the midline These animals exhibit cephalization concentration of sensory organs a brain in a well-defined head definite anterior (head) region definite posterior (which may feature a tail) region
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Body Symmetry and Cephalization Fig. 23-2 (a) Radial symmetry (b) Bilateral symmetry central axis anterior posterior plane of symmetry plane of symmetry
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Most bilateral animals have body cavities
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  • Spring '08
  • pomarico
  • Biology, Crossword Puzzles, Test Reviews, Cnidaria, Phylum, Annelid

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