Chapter 22

Chapter 22 - Chapter 22: Animal Diversity I, Invertebrates...

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Chapter 22: Animal Diversity I, Invertebrates
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Key Features of Animals Animals possess all of the following characteristics Multicellularity Heterotrophic Cells lack a cell wall Are able to respond rapidly to external stimuli Most animals populating the Earth were present by the Cambrian period (544 million years ago
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Animal Evolution Certain features represent evolutionary milestones: The appearance of tissues The appearance of body symmetry Protostome and deuterostome development These features mark major branching points on the animal evolutionary tree
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Porifera (sponges) Cnidaria (jellyfish, corals, anemones) Ctenophora (comb jellies) Arthropoda (insects, arachnids, crustaceans) Platyhelminthes (flatworms) Annelida (segmented worms) Mollusca (clams, snails, octopods) Echinodermata (sea stars, sea urchins) Chordata (lancelets, vertebrates) cuticle molted protostome development deuterostome development bilateral symmetry radial symmetry no tissues tissues Nematoda (roundworms) 0 PRIMITIVE ANCESTOR
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The Appearance of Tissues Tissues are groups of similar cells that carry out a specific function (e.g. muscle) The earliest animals had no tissues Sponges are the only modern-day animals that lack tissues Individual cells may be specialized, but they act independently Sponges and other phyla arose from and ancient common ancestor without tissues 3 types of layers…
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Animal Tissues Ectoderm (top) Endoderm (bottom) Mesoderm (middle)
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The Appearance of Body Symmetry Symmetrical animals have an upper (dorsal) surface and a lower (ventral) surface Animals with tissues exhibit either radial or bilateral symmetry 3 types Radial, bilateral, asymmetric (no symmetry)
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Radial Symmetry Can be divided into roughly equal halves by any plane that passes through the central axis Have two embryonic tissue (germ) layers: Ectoderm (outer layer, covers the body) Endoderm (inner layer, lines most hollow organs. Tend to be either sessile (fixed on one spot) or “free floating”, drift around on currents Cnidarians, hydra
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Radial symmetry central axis plane of symmetry
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radial symmetry
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Bilateral Symmetry Can be divided into mirror-image hales only along one plane that runs down the midline Have an additional germ layer: Mesoderm (middle layer, forms muscle and circulatory/skeletal system) Exhibit cephalization (concentration of sensory organs and brain in a well defined head) Defined anterior (head) and posterior (tail) regions
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Bilateral symmetry anterior plane of symmetry posterior
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dorsal anterior posterior ventral bilateral symmetry
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Body Cavities Most bilateral animals have a body cavity Serve many functions Skeleton:
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This note was uploaded on 05/04/2010 for the course BIOL 1002 taught by Professor Pomarico during the Spring '08 term at LSU.

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Chapter 22 - Chapter 22: Animal Diversity I, Invertebrates...

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