Information AboutBody Cavity |
| CATEGORIES ABOUT BODY CAVITY | |
| animal anatomy | |
| developmental biology | |
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The type of body cavity places an organism into one of these three groups:
COELOM A coelom is a cavity lined by an Epithelium derived from Mesenchyme . Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks. This key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. Arthropod s and Mollusk s have a reduced (but still true) coelom. Their principal body cavity is the ''hemocoel'' of an Open Circulatory System . Mammalian embryos develop two coelomic cavities: the intraembryonic coelom and the extraembryonic coelom (or Chorionic Cavity ). The intraembryonic coelom is lined by somatic and splanchnic lateral plate mesoderm, while the extraembryonic coelom is lined by extraembryonic mesoderm. The intraembryonic coelom is the only cavity that persists in the mammal at term, which is why its name is often contracted to simply ''coelomic cavity''. Subdividing the coelomic cavity into compartments, for example, the Pericardial Cavity , where the heart develops, simplifies discussion of the Anatomies of complex animals. Formation In animals of the Phyla Annelid a, Mollusca, and Arthropoda, the mesoderm forms as a mass of tissue from special embryonic cells between the ectoderm and the endoderm. This mesodermal mass then splits to form the coelom. In Deuterostome s, mesoderm arises out of folds in the developed endoderm which pinch off to form the coelom. Origins The origin of the coelom is uncertain. The oldest known animal to have had a body cavity is Vernanimalcula . Current Evolutionary theories:
PSEUDOCOEL In some Protostome s, the embryonic Blastocoele persists as a body cavity. These protostomes have a fluid filled main body cavity unlined or partially lined with tissue derived from mesoderm. This fluid-filled space surrounding the internal Organ s serves several functions like distribution of nutrients and removal of waste or supporting the body as a Hydrostatic Skeleton . Pseudocoelomates : '' Pseudocoelomate is no longer considered a valid Taxonomic Group , since it is not Monophyletic . However, it is still used as a descriptive term.'' A pseudocoelomate is any Invertebrate Animal with a three-layered body and a pseudocoel. The coelom was apparently lost or reduced as a result of Mutation s in certain types of Gene s that affected early development. Thus, pseudocoelomates evolved from coelomates ( Evers , 355). Important characteristics:
Examples of pseudocoelomates
NO COELOM Lacking a fluid filled body cavity presents some serious disadvantages. Fluids do not compress, while the tissue surrounding the organs of these animals will compress. Therefore, acoelomate organs are not protected from crushing forces applied to the animal’s outer surface. HUMAN BODY CAVITIES REFERENCES
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