Biology: Coelomates

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Coelomates: Animals with Internal Body Cavities | Back to Top Coelomates are animals that have internal body cavities, or coeloms. Humans are coelomates, we have an abdomenal cavity (digestive organs, some of the excretory and reproductive organs) and a thoracic cavity (heart and lungs). Coelomates also form a variety of internal and external skeletons. External skeletons and coeloms appeared during the Cambrian-Ordovician time, as shown in Figure 1. These skeletons offered several advantages to their producers: 1. Secretion of a mineral shell that allowed the animal to use the shell as a mineral repository. 2. Protection from drying out in the intertidal zone during low tides. 3. Protection from predators. 4. Sites for anchoring muscle attachments, offering new patterns of locomotion and increased strength. Figure 1. First appearances and relative diversity (width of shaded area) for major groups of animals. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. | | Phylum Mollusca: Clams, Scallops, and Squids | Back to Top The phylum Mollusca contains over 100,000 species with a variety of body forms and lifestyles. In mollusks, the coelom is reduced and limited to the region around the heart. The Mollusk body first appeared during the Cambrian Period. All mollusks have: 1. a visceral mass containing internal organs, including the digestive tract, paired kidneys, and reproductive organs. 2. a mantle that surrounds but does not cover entirely the visceral mass and secretes a shell (if one is present). The mantle also contributes to formation of gills or lungs. 3. a head/foot region containing sensory organs and a muscular structure (foot) used for locomotion. The foot is a muscular structure used for locomotion,

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