1 Animals - Animal diversity The focus of the next few...

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Unformatted text preview: Animal diversity The focus of the next few lectures is on animals. We begin with an overview of their diversity, emphasizing a few selected groups of animals, then move to a discussion of their form and function. Animals are multicellular, heterotrophic organisms that ingest their food and use internal enzymatic breakdown. In this regard, animals differ from fungi, which are also heterotrophic, but absorb food materials after external enzymatic breakdown. To illustrate the diversity of animals and the major innovations that characterize their evolution, I highlight six major groups, with an emphasis on the chordates. Please read pages 670-688, 700-702, 705-713, and 718-738 in the text for a more detailed discussion of the various groups. Sponges Sponges have a simple body plan, with a cellular level of organization. They consist of loose aggregations of cells built around a central water canal system. Sponges are aquatic and sessile. They are also commonly asymmetrical, in that their bodies cannot be divided along a plane into similar halves. Sponges contain distinctive feeding cells called choanocytes, which have a collar and flagellum, as illustrated in Figure 31.7 in the text. Beating of the flagella causes water to flow into the sponge, where food particles are captured by the choanocytes. Cnidarians Cnidarians include hydrozoans, jellyfishes, sea anemones, and corals. Cnidarians have a tissue level of organization. The body wall in cnidarians is differentiated into two distinct tissue layers: an outer ectoderm and an inner endoderm....
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1 Animals - Animal diversity The focus of the next few...

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