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Unformatted text preview: LS1 Demonstration Mullosks, Arthropods, and Echinoderms Page 1 of 15 WEEK 8: MOLLUSKS, ARTHROPODS AND ECHINODERMS Introduction This week we continue our sampling of animal diversity. We will look at three phyla showing different animal radiations: Mollusca (in the lophotrochozoan clade of the protostomes), Arthropoda (in the ecdysozoan lineage of the protostomes), and the Echinodermata (the first groups of deuterostomes). While these phyla represent very distinct lineages, they do share some characteristics and some suites of adaptations. You have the opportunity to examine how different phylogenetic histories can affect the traits that we see in these groups. Using table 7.2 from last weeks lab, continue your comparisons of animal phyla. Are there common solutions to common problems? Do the features that you have recorded tell you much about the evolutionary relationships between the phyla? Can you think of other traits that would tell you more about these relationships? Phylum Mollusca Mollusks are an important and interesting groups of animals. Their impressive evolutionary radiation has resulted in more than 75,000 extant species. Mollusks have an extensive fossil record, and much of what we know about past changes in climate and mass extinctions comes from mollusk fossils. Whereas many mollusks are marine, a large number of species have diversified in freshwater and terrestrial habitats. In fact, there are far more terrestrial mollusk species (35,000) than terrestrial vertebrates (25,000). In the mid-ocean, particularly in the abyssal depths, mollusks are the large dominant predators. Many mollusks have developed complex nervous and sensory systems and possess reasoning and problem solving abilities unmatched by any other invertebrate group and even many vertebrates. Mollusks have distinct bilateral symmetry and an internal body cavity. Mullosks have radiated from an ancestral form with the following key traits (fig 8.1): 1. A muscular foot, used in locomotion, which is attached to the head 2. A specialized part of the body wall called the mantle, which often secretes a hard shell 3. A visceral mass containing the major organs 4. A calcium carbonate shell 5. A rasping tongue-like feeding structure call a radula . As you examine mollusks in lab today, think about how these traits have been modified through evolution. LS1 Demonstration Mullosks, Arthropods, and Echinoderms Page 2 of 15 Fig 8.1 generalized molluscan body plan Exercise 1: Chitons Chitons (figure 8.2) are common on rocky intertidal habitats like those you can easily find along the California coast. Most chitons are marine herbivores that scrape algae from rocks using a radula. Chitons firmly attach themselves to the surface of rocks using their muscular, mucus- covered foot....
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- Spring '05