Coelomic Development Essay

631 Words3 Pages
DISCUSS THE FUNCTIONAL AND PHYLOGENETIC SIGNIFICANCE OF A TRUE BODY CAVITY (COELOM OR PSEUDOCOEL) IN THE BIOLOGY OF ANIMALS Most animal phyla originated in a relatively brief span of geological time; however the diversity among them is extraordinary. Every organism is very unique and detailed in certain ways; comparisons of certain types of organisms can be very difficult. In echinoderms and chordates, the anus forms first and is then followed by the mouth, this makes them deuterostomes. In other phyla such as annelids and molluscs, the mouth forms first, making them protostomes. In the past, zoologists grouped animals based on characteristics related to the coelom and this is where the coelom body cavity gained some of its importance. The presence or absence of a coelom and the way it was formed was believed to be important in understanding the phylogenetic relationships of animal phyla. However, recent molecular phylogenies have suggested this characteristic is not as informative as previously believed: the coelom may have arisen twice, once in protostomes and once among deuterostomes. A coelom is a fluid-filled cavity which is derived from mesoderm. The peritoneal cavity in a human abdomen is one part of our coelom, and there are similar spaces around our heart and lungs. Coelom formation begins in the gastrula stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron. In protostomes the coelom forms by a process known as schizocoelous. The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall, and the second surrounds the endoderm forming the visceral layer or alimentary canal. The space between the two layers is known as the coelom or body cavity. In deuterostomes, the coelom formation is enterocoelous; mesoderm buds from the walls of the archenteron and hollows to

More about Coelomic Development Essay

Open Document