rav65819_ch32_621-634

rav65819_ch32_621-634 - ;;;;;;;; 32 chapter introduction...

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Unformatted text preview: ;;;;;;;; 32 chapter introduction Overview of Animal Diversity WE NOW EXPLORE THE GREAT diversity of modern animals, the result of a long evolutionary history. Animals are among the most abundant living organisms. Found in almost every conceivable habitat, they bewilder us with their diversity. More than a million species have been described, and several million more are thought to await discovery. Despite their great diversity, all animals have much in common. For example, locomotion is a distinctive characteristic of higher animals, although not all animals move about. Early naturalists thought that sponges and corals were plants because the adults seemed rooted to one place and did not move about. Biologists have long debated the evolutionary relationships among animal groups and have traditionally used information derived from their anatomy and especially from their early embryonic development. For the last two decades, molecular tools have provided new insights; together with the recent synthesis of evolutionary and developmental biology (chapter 25) and the discovery of new and mysterious forms of life, these new data are leading biologists to reconsider the animal tree of life. concept outline 32.1 Some General Features of Animals 32.2 Evolution of the Animal Body Plan Tissues evolved, allowing specialized functions Most animals exhibit radial or bilateral symmetry A body cavity made possible the development of advanced organ systems Bilaterians exhibit two main types of development Segmentation allowed redundant systems and more efFcient locomotion 32.3 The Traditional Classication of Animals Presence of tissues and symmetry separated the Parazoa and Eumetazoa Symmetry and embryonic layers distinguished diploblasts from triploblasts urther divisions were based on other key features 32.4 A New Look at the Metazoan Tree of Life The myzostomids have defed classifcation: A case study Molecular systematics is changing our understanding oF animal phylogency 32.5 Evolutionary Developmental Biology and the Roots of the Animal Tree of Life Metazoans appear to have evolved From colonial protists Molecular analysis may explain the Cambrian explosion 621 rav65819_ch32_621-634.indd 621 rav65819_ch32_621-634.indd 621 12/7/06 2:03:36 PM 12/7/06 2:03:36 PM 32.1 Some General Features of Animals Animals are the eaters, or consumers, of the Earth. Animals are a very diverse groupno one criterion fits allbut several characteristics are of major importance: Animals are heterotrophs and must ingest other organisms for nourishment. All animals are multicellular. Unlike plants, fungi, and certain protists, animal cells lack cell walls; in addition, unlike protists, animals have specialized cells that form tissues or organs....
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This note was uploaded on 10/15/2010 for the course BIO BIO1 taught by Professor Lipke during the Fall '09 term at CUNY Brooklyn.

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rav65819_ch32_621-634 - ;;;;;;;; 32 chapter introduction...

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