Biology 2 Chapter 4

Biology 2 Chapter 4 - Chapter 22: Animal Diversity I,...

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Unformatted text preview: Chapter 22: Animal Diversity I, Invertebrates 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) 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 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) PRIMITIVE ANCESTOR For exam, know scientific phylum name and common name 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 an ancient common ancestor without tissues 3 types of layers Animal Tissues Ectoderm (top) Endoderm (bottom) Mesoderm (middle) 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) 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 to one spot) or free floating, drift around on currents Cnidarians, hydra Radial symmetry central axis plane of symmetry radial symmetry Bilateral Symmetry Can be divided into mirror-image halves only along one plane that runs down the midline Have an additional tissue layer: Mesoderm (middle layer, forms muscle & circulatory/skeletal system) Exhibit cephalization (concentration of sensory organs & brain in a well-defined head) Defined anterior (head) and posterior (tail) regions Bilateral symmetry anterior plane of symmetry posterior d o r s a l a n t e r i o r p o s t e r i o r v e n t r a l bilateral symmetry Body Cavities Most bilateral animals 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, acoelomate Body Cavity Structure Varies...
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Biology 2 Chapter 4 - Chapter 22: Animal Diversity I,...

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