Chapter 22

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

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Unformatted text preview: Chapter 22: Animal Diversity I, Invertebrates Key Featur es 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 The Appear ance 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… Animal Tissues • Ectoderm (top) • Endoderm (bottom) • Mesoderm (middle) The Appear ance of Body Symmetr y • 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 Symmetr y • Can be divided into roughly equal halves by any plane that passes through the central axis • Have two embryonic tissue (germ) layers: – Ectoder m (outer layer , cover s the body) – Endoder m (inner layer , lines most hollow or gans. • Tend to be either sessile (fixed on one spot) or “free floating”, drift around on currents Radial symmetry central axis plane of symmetry radial symmetry Bilater al Symmetr y • Can be divided into mirror-image hales only along one plane that runs down the midline • Have an additional germ layer: – M esoder m (middle layer , for ms muscle and cir culator y/skeletal system) • Exhibit cephalization (concentration of sensory organs and brain in a well defined head) • Defined anterior (head) and posterior 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...
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This note was uploaded on 03/12/2010 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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