metameric segmentation The repetition of organs and tissues at intervals along the body of an animal, thus dividing the body into a linear series of similar parts or segments (metameres). It is most strikingly seen in Annelida. Essentially, metameric segmentation is an internal, mesodermal phenomenon, the body musculature and coelom being the primary segmental divisions; this internal segmentation imposes a corresponding segmentation on the nerves, blood vessels, and excretory organs. In some metameric animals the segmentation is visible externally but in others (e.g. Chordata) external segmentation has been lost and internal segmentation is best seen in the embryo. Metameric segmentation is thought to have arisen as an adaptation to more efficient locomotion.
metameric segmentation (metamerism; segmentation) The division of an animal's body (except at the head region – see cephalization) into a number of compartments (segments or metameres) each containing the same organs. Metameric segmentation is most strongly marked in annelid worms (e.g. earthworms), in which the muscles, blood vessels, nerves, etc. are repeated in each segment. In these animals the segmentation is obvious both externally and internally. It also occurs internally in arthropods and in the embryonic development of all vertebrates, in which it is confined to parts of the muscular, skeletal, and nervous systems and does not show externally.
More From encyclopedia.com
Animal , Animal Animals are creatures in the kingdom Animalia, one of the five major divisions of organisms. They are multicelled, eukaryotic (pronounced yook… Coelom , coelom A fluid-filled (see COELOMIC FLUID) body cavity that originates by the splitting of the mesoderm of triploblastic animals. It separates the mu… Pseudocoelomate , pseudocoelomate Describing any invertebrate animal whose body cavity is a pseudocoel, a cavity between the gut and the outer body wall derived from a… Animalia , The kingdom Animalia, or Metazoa, includes all animals. Animals are multicellular, eukaryotic organisms, which are heterotrophic, meaning they obtain… Metazoan , In the tenth edition of his book Systema Naturae (1758), Swedish botanist Carolus Linnaeus developed a biological classification system (now known as… Locomotion , Animals have evolved an amazing variety of ways to get around. There are animals with no legs; animals with one appendage that serves as a "leg" (sna…
About this article
All Sources -
Updated Aug 08 2016 About encyclopedia.com content Print Topic
You Might Also Like