Lab 10 Animal Diversity Invertebrates

Lab 10 Animal Diversity Invertebrates - Page | 1 Tiffany...

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P a g e | 1 Tiffany Nguyen November 26, 2008 The Regenerative Properties of Planarian [ Introduction ] About 95% of animal species are invertebrates (Campbell and Reese, 2008). “Many invertebrates are marine and their body forms and lifestyles reflect their early origin in the primitive seas” (Lum et al., 2008). The invertebrate group can be broken down, simply, into two groups of organisms, the more primitive protostomes and the more advanced deuterostomes. There are four fundamental differences between these two groups. Protostomes have spiral cleavage and their coelom is formed by mesoderm splitting. Also, their blastospore eventually becomes their mouth. Deuterostomes have radial cleavage and their coelom is formed by mesodermal pouches. Also, their blastospore eventually becomes their anus. However, the difference that is most relevant to this lab is the fact that protostomes have determinate cleavage while deuterostomes have indeterminate cleavage. This means that the cells of protostomes have a fixed fate while those of the deuterostomes can be altered if they are caught at a certain point in development (Lum et al., 2008). One certain group of invertebrates, the planarians, along with tapeworms and flukes, belong to the phyla Platyhelminthes. This phylum alone has about 20,000 species. Platyhelminthes have bilateral symmetry and a central nervous system; however, they have no body cavity or organs for circulation (Campbell and Reese, 2008). Planarians, the focus in this lab, generally live in clean freshwater ponds and streams and feed on either smaller or dead animals. They will move using cilia on their ventral surface and are aided by the film of mucus
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P a g e | 2 that they secrete as they move along (Campbell and Reese, 2008). Instead of eyes, planarians
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