Biology+Ch+22

Biology+Ch+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 Multicellular heterotrophic cells lack a cell wall are able to respond 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 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 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 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 Symetrical animals have upper surface (dorsal) and lower (ventral) surface Animals with tissues exhibit either radial symetry or bilateral symmetry 3 types Radial, bilateral, asymetric (no Symetry)
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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 sessile (fixed to one spot) or drift around on currents Cnidarians (jellyfish) 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 halves only along one plane that runs down the middle Have an additional germ layer Mesoderm (middle layer, forms muscle and circulatory /skeletal system) Exhibit cephalization (concentration of 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 organisms have a body cavity Serve many functions Skeleton: provides support and a framework against which muscles can act) Protection: Buffer between internal organs and the outside world 3 types Coelomate (eucoelomate), pseudocoelomate, acoelomates
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Biology+Ch+22 - Chapter 22 Animal Diversity I Invertebrates...

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