IV-Unit- Dr.M.Deivanayaki Exoskeleton Exoskeleton Definition An exoskeleton is the rigid covering found on the exterior of many animals, particularly invertebrates such as arthropods and mollusks. Much like the internal endoskeleton of
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IV-Unit- Dr.M.Deivanayaki Exoskeleton<br>
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Exoskeleton Definition
An exoskeleton is the rigid covering found on the exterior of many animals, particularly invertebrates such as arthropods and mollusks.
Much like the internal endoskeleton of vertebrates, the exoskeleton is responsible for supporting the structure of an animal’s body.
The exoskeleton also provides protection against attack from predators, and accidental damage of the soft internal organs. Furthermore, due to the waterproof qualities of the skeletal tissues, an exoskeleton acts as a barrier and protects organisms from desiccation.
In arthropods, the muscles are attached directly to the interior of the exoskeleton—unlike in vertebrate endoskeletons, where the muscles are connected to the skeleton via tendons and ligaments. This direct connection means that there is a larger surface area for the muscle to attach to, allowing for powerful movement and strength. Additionally, jointed limbs, which connect the hard exterior plates, permit a wide range of available movements.<br>
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Exoskeleton is a hard, external structure that covers, supports, and protects an animal's body, such as the chitinous covering of a crab, the silica shells (frustules) of diatoms, or the calcareous shells, or valves, of bivalve mollusks. The term exoskeleton is used in contrast to the endoskeleton, or internal support structure, that provides body structure and shape to such animals as chordates and echinoderms.
While the term exoskeleton most commonly is used for invertebrates, such as arthropods, it is sometimes extended to such vertebrate structures as the shell of turtles and the hard covering of many groups of fossil fishes (such as the placoderms) (Gilbert et. 2007). Types and description
Many taxa produce exoskeletons, which may be composed of a range of materials, including chitin, calcium carbonates, silica, bone, cartilage, and dentine. Organisms range from the microscopic diatoms and radiolaria to the innumerable species of arthropods, to vertebrates such as turtles. Exoskeletons appear to have arisen independently many times, with eighteen lineages involving calcified exoskeletons alone (Porter 2007). Arthropod exoskeleton
The tough or resistant exoskeleton of arthropods (insects, crustaceans, and so on) typically is constructed of the tough polymer of chitin<br>
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Vertebrate exoskeletons
Bone, cartliage, and dentine are used for the exoskeleton in vertebrates such as the Ostracoderm fish and turtles. Turtles, for example, have a special bony or cartilaginous shell. While some consider the turtle shell not to be an exoskeleton, on the basis of it being a modified ribcage and part of the vertebral column (Ardastra 2008; Martinelli 2007), others are specific that the turtle shell and the covering of fossil fishes (particularly placoderms) are indeed an exoskeleton (Smith and Hall 1993; Gilbert et al. 2007). Indeed, Gilbert et al. (2007) includes the cranial and facial dermal bones as part of the vertebrate exoskeleton, and attribute their being derived from the neural crest cells.
Furthermore, other lineages have produced tough outer coatings analogous to an exoskeleton, such as some mammals—constructed from bone in the armadillo, and hair in the pangolin—and reptiles such as crocodiles with their bony scutes and horny scales.<br>
