A hydrostatic skeleton is a skeleton created by a fluid-filled compartment within the body, dubbed the coelom. The organs of the coelom room supported through the aqueous fluid, which also resists exterior compression. This compartment is under hydrostatic pressure due to the fact that of the fluid and also supports the various other organs the the organism. This form of skeletal mechanism is uncovered in soft-bodied animals such together 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 example of a hydrostatic skeleton. (credit: “Amada44”/Wikimedia Commons)

one exoskeleton is an external skeleton that consists of a difficult encasement on the surface ar of one organism. For example, the shells the crabs and insects space exoskeletons (Figure 19.3). This skeleton kind provides defence against predators, supports the body, and enables for movement through the contraction of attached muscles. Just like vertebrates, muscles must cross a joint within the exoskeleton. Shortening the the muscle alters the connection of the 2 segments of the exoskeleton. Arthropods such together crabs and also lobsters have exoskeletons that consist that 30–50 percent chitin, a polysaccharide derivative that glucose the is a solid but functional material. Chitin is secreted by the epidermal cells. The exoskeleton is further strengthened through the addition of calcium lead carbonate in biology such together the lobster. Since the exoskeleton is acellular, arthropods should periodically burned their exoskeletons since the exoskeleton does not prosper as the organism grows.

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

an endoskeleton is a skeleton that is composed of hard, mineralized structures situated within the soft organization of organisms. An instance of a primitive endoskeletal framework is the spicules that sponges. The skeletal of vertebrates room composed of tissues, whereas sponges have no true organization (Figure 19.4). Endoskeletons carry out support for the body, defend internal organs, and permit for motion through contraction of muscle attached come the skeleton.

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Figure 19.4. The skeletons the humans and horses are examples of endoskeletons. (credit: Ross Murphy)
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The axial skeleton creates the central axis the the body and also includes the bones of the skull, ossicles that the center ear, hyoid bone that the throat, vertebral column, and the thoracic cage (ribcage) (Figure 19.5). The duty of the axial skeleton is to administer support and also protection for the brain, the spinal cord, and the offal in the ventral human body cavity. It provides a surface for the attachment of muscle that move the head, neck, and trunk, performs respiratory tract movements, and stabilizes parts of the appendicular skeleton.

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Figure 19.5. The axial skeleton is composed of the skeleton of the skull, ossicles that the center ear, hyoid bone, vertebral column, and also rib cage. (credit: modification of work-related by Mariana Ruiz Villareal)