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The Class Polyplacophora

The Class Polyplacophora - commonly found as fossils One...

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The Class Polyplacophora Chitons, shown in Figure 3, are in the taxonomic class Polyplacophora. They have a shell consisting of eight overlapping plates. A ventral muscular foot is used for creeping along the substrate, or for clinging to rocks. A chiton feeds by scraping algae and other plant food from rocks with its well-developed radula. The Class Gastropoda The class Gastropoda includes snails, terrestrial slugs, whelks, conchs, periwinkles, sea hares, and sea slugs. Most gastropods are marine , although some there are freshwater and terrestrial forms. Many gastropods are herbivores that use their radula to scrape food from surfaces. Carnivorous gastropods use their radula to bore through a surface, such as a bivalve shell, to obtain food. Most gastropods have a well developed head with eyes and tentacles projecting from a coiled shell that protects the visceral mass, as shown in Figure 4. The coiled shells of gastropods are often quite
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Unformatted text preview: commonly found as fossils. One genus, Turetella , occurs in such quantities in a type of rock that the rock is known as " Turetella agate". However, not all gastropods have shells, the nudibranchs (sea slugs) and terrestrial slugs lack shells. In aquatic gastropods, gills are found in the mantle cavity; in terrestrial gastropods, the mantle is richly supplied with blood vessels and functions as a lung when air is moved in and out through respiratory pores. Terrestrial gastropod embryonic development does not go through a swimming larval stage, as is the case in aquatic gastropods. For terrestrial snails, their shell not only offers protection but also prevents desiccation (drying out). The muscular foot contracts in peristaltic waves from anterior to posterior causing secretion of a lubricating mucus....
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