noun, plural: coeloms
(2) A body cavity
Animals may be grouped based on the coelom:
Coelom is a crucial step in evolution since a complicated body plan would benefit from it. A coelom allows compartmentalization to separate biological systems that carry out differing major functions. For instance, animals without coelom (acoelomates) would have to rely on diffusion to transport nutrients around the body. Since acoelomates (such as flatworms) are relatively small and have less intricate body plan (flat), diffusion is enough to carry out transport function. However, for animals (such as mammals) that have complicated body plans would need other transport system (circulatory system) apart from diffusion. A coelom would therefore be useful to separate circulatory system from abdominal organs that carry out a different major function (which is digestion). Thus, both of these systems can perform their function separately and with more efficiency. Coelom also allows organs to grow and change in position or shape.
Word origin: Greek koilōma (cavity)