A hydrostatic skeleton is a skeleton developed by a fluid-filled compartment in ~ the body, dubbed the coelom. The offal of the coelom room supported by the aqueous fluid, which additionally resists exterior compression. This compartment is under hydrostatic pressure due to the fact that of the fluid and supports the other organs the the organism. This form of skeletal system is discovered in soft-bodied animals such as sea anemones, earthworms, Cnidaria, and other invertebrates (Figure 19.2).

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Figure 19.2. The skeleton that the red-knobbed sea star (Protoreaster linckii) is an instance of a hydrostatic skeleton. (credit: “Amada44”/Wikimedia Commons)

an exoskeleton is an exterior skeleton that is composed of a tough encasement top top the surface ar of an organism. For example, the shells that crabs and also insects are exoskeletons (Figure 19.3). This skeleton kind provides defence against predators, supports the body, and enables for movement through the convulsion of enclosed muscles. As with vertebrates, muscles need to cross a joint within the exoskeleton. Shortening that the muscle changes the connection of the two segments the the exoskeleton. Arthropods such together crabs and also lobsters have actually exoskeletons that consist that 30–50 percent chitin, a polysaccharide derivative the glucose the is a solid but flexible material. Chitin is secreted by the epidermal cells. The exoskeleton is more strengthened by the enhancement of calcium carbonate in biology such as the lobster. Due to the fact that the exoskeleton is acellular, arthropods must periodically melted their exoskeletons due to the fact that the exoskeleton walk not prosper as the biology grows.

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Figure 19.3. Muscles attached to the exoskeleton the the Halloween crab (Gecarcinus quadratus) permit it come move.

an endoskeleton is a skeleton that consists of hard, mineralized structures situated within the soft organization of organisms. An example of a primitive endoskeletal structure is the spicules that sponges. The bones of vertebrates space composed that tissues, conversely, sponges have actually no true organization (Figure 19.4). Endoskeletons provide support for the body, protect internal organs, and enable for motion through convulsion of muscle attached come the skeleton.

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Figure 19.4. The skeletons of humans and also horses are examples of endoskeletons. (credit: Ross Murphy)
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The axial skeleton develops the central axis the the body and also includes the skeletal of the skull, ossicles the the middle ear, hyoid bone of the throat, vertebral column, and also the thoracic cage (ribcage) (Figure 19.5). The duty of the axial skeleton is to provide support and protection for the brain, the spinal cord, and the guts in the ventral human body cavity. It offers a surface for the attachments of muscles that relocate the head, neck, and also trunk, performs respiratory tract movements, and stabilizes parts of the appendicular skeleton.

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Figure 19.5. The axial skeleton consists of the skeletal of the skull, ossicles of the middle ear, hyoid bone, vertebral column, and rib cage. (credit: change of job-related by Mariana Ruiz Villareal)