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A body cavity is an aspect of a number of basic animal body plans ( phyla) that incorporate a central body cavity, known as a coelom. The coelom contains major organs, including the digestive system, heart, kidneys, etc. The coelom has two openings for the input of food and ejection of waste. It is filled with liquid that acts as a lubricant allowing the visceral organs to move freely relative to one another.The most common body plans for large mobile animals fall into a group called the Bilateria. They include the annelids, arthropods, chordates, vertebrates, echinoderms, and mollusks. All have a cavity known as a coelom -- presumably inherited from a common ancestor. They are divided into two groups based on whether the first opening in the coelom cell wall during development of the animal becomes the anus or the mouth. In protostomes, the opening becomes the mouth. Protostomes include annelids, arthropods and mollusks. In Deuterostomes, the opening becomes the anus. Chordates and echinoderms are both Deuterostomes.
In arthropods and mollusks, the coelom is reduced in size, and the principal body cavity is part of the bloodBlood is a circulating tissue composed of fluid plasma and cells ( red blood cells, white blood cells, platelets). Medical terms related to blood often begin in hemo or hemato ( BE: haemo and haemato from the Greek word for "blood". Blood of different spe circulation system called a haemocoel .
The coelom may be subdivided into "subcavities" such as the pericardial cavity around the heart. The number and placement of these divisions are useful in the classification of, for example, the vertebrates.
These relatively obscure details are important to evolutionary theoryThis article is about biological evolution. For other possible meanings, see Evolution (disambiguation). Evolution generally refers to any process of change over time. However, in the context of the life sciences, evolution is a change in the genetic make. It is presumed that the bilateria evolved from a single common ancestor, and that the division between protostomes and deuterostomes represents an early step in that evolution. Since fossilFor other uses of the term, see Fossil (disambiguation Fossils are the mineralized remains of animals or plants or other artifacts such as footprints. The totality of fossils and their placement in rock formations and sedimentary layers is known as the fo evidence from that remote period is fragmentary and not always helpful, the analysis of animal development provides additional clues to the evolution of multi-celled animals. The origin of the coelom is unknown. It has been proposed that it developed within a group of organisms known as acoelomatesAcoelomates consist of two modern phyla of worms the Platyhelminthes and Nemerteans. These animals are quite common with perhaps 20,000 species known. Some are free living. Many are parasitic. Although the acoelomates are triploblastic with three germ lay via some members of another group known as "pseudocoelomates". Alternatively, it is thought that the coelom may have evolved from gastric pouches ("stomachs" sort of) in cnidariansAnthozoa Corals and sea anemones Cubozoa Sea wasps or box jellyfish Hydrozoa Hydroids, hydra-like animals Scyphozoa Jellyfish The cnidarians are a phylum of some 10,000 species of relatively simple animals, found exclusively in aquatic environments (most.
See http://www.gwu.edu/~darwin/BiSc151/Coelom/Coelom.html for a discussion in greater depth including diagrams.
AnatomyAnatomy (from the Greek anatome from ana-temnein to cut up), is the branch of biology that deals with the structure and organization of living things; thus there is animal anatomy ( zootomy) and plant anatomy ( phytonomy). The major branches of anatomy in
