A hydrostatic skeleton or hydroskeleton is a structure found in many soft-bodied invertebrates consisting of a fluid-filled cavity, the coelom, surrounded by muscles. The pressure of the fluid and action of the surrounding muscles are used to change an organism's shape and produce movement, such as burrowing or swimming. Hydrostatic skeletons have a role in the locomotion of echinoderms (starfish, sea urchins), cnidarians (jellyfish), annelids (earthworms), nematodes, and other invertebrates
An endoskeleton is an internal support structure of an animal. In three phyla and one subclass of animals, endoskeletons of various complexity are found: Chordata, Echinodermata, Porifera and Coleoidea. An endoskeleton allows the body to move and gives the body structure and shape. A true endoskeleton is derived from mesodermal tissue. Such a skeleton is present in echinoderms and chordates. The poriferan 'skeleton' consists of microscopic calcareous or siliceous spicules or a spongin network. The Coleoidae do not have a true endoskeleton in the evolutionary sense; here, a mollusc exoskeleton evolved into several sorts of internal structure, the "cuttlebone" of cuttlefish being the best-known version
An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animal's body. All arthropods (such as insects, spiders and crustaceans) and many other invertebrate animals (such as shelled mollusks) have exoskeletons. Lobsters, for example, have tough outer shell systems which provide rigidity and shape to their bodies, in addition to an endoskeleton. The endoskeleton of arthropods is continuous with and an extension of the exoskeleton and is shed at the same time as the exoskeleton.
An insect's exoskeleton (integument) serves not only as a protective covering (armour) over the body but also as a surface for muscle attachment, a water-tight barrier against desiccation and a sensory interface with the environment. It is a multi-layered structure with four functional regions: epicuticle, procuticle, epidermis and basement membrane.
while the arthropod exoskeleton is chitin-based, it is not composed entirely of chitin. In fact, the membranous portions of the exoskeleton and endoskeleton are closer to pure chitin than the hardened external sclerites.
2007-02-07 07:08:49
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answer #1
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answered by MSK 4
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Hydrostatic skeleton: primitive skeletal structure: the most primitive form of skeletal structure, found in animals such as jellyfish and worms, that consists of layers of muscle around a fluid-filled body cavity
Exoskeleton
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A form of exoskeleton is the shell of calcium or silica secreted by certain protozoans known as foraminiferans. Commercial sponges have an exoskeleton consisting of spongin, which is a tough, elastic substance. Cnidarians secrete a wide variety of exoskeletal substances, ranging from the elastic covering of the jellyfish to the stony material deposited by coral. The familiar shells of most mollusks are composed of calcium carbonate and an organic ground substance known as conchiolin. Among insects, each of the three principal divisions of the body—the head, the thorax, and the abdomen—is enclosed in a framework of horny plates. The plates of each primary division are separated from those of the next division by elastic tissue that permits flexibility of motion. The appendages are enclosed by sheaths projecting from the exoskeleton; elastic tissue similar to that between the plates joins the segments of the appendages and attaches them to the body.
III Endoskeleton
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Vertebrates have a more or less rigid group of structures composed of cartilage or bone or of a combination of these two connective tissues. The most primitive of these structures is the notochord, which is a backbone of cartilage occurring in fishes. Animals higher on the evolutionary scale have an axial skeleton, consisting of the skull, spinal column, and ribs, and an appendicular skeleton, made up of the pelvic and pectoral girdles and the appendages.
In higher animals, the skeleton formed in the embryo is initially cartilaginous; bone and calcium are deposited as the organism matures. In humans, the process of bone hardening, or ossification, is completed at about the age of 25. The last bone to ossify is the breastbone.
2007-02-07 05:19:11
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answer #2
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answered by Nikki 1
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