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the slender transverse partitions in the coelom of metameric invertebrate animals, such as segmented worms. Dissepiments form by the joining of the adjacent walls of paired coelomic cavities arranged one behind the other. Contraction of the muscles of the dissepiments and of the musculocutaneous sac causes pressure changes in the cavity fluid. Dissepiments are most pronounced in polychaete and oligochaete worms, and they are absent in leeches.