Metameres


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Related to Metameres: metameric segmentation

Metameres

The serial repetition of parts along the length of the body axis in bilaterally symmetrical animals. The successive subdivisions are called metameres, somites, or segments, hence the synonym, segmentation. Common examples are the muscles and spinal nerves in the human body and in the body and tail of many mammals, snakes and lizards, salamanders, and fishes. It also occurs in other chordates, and in arthropods and annelid worms. It never involves reproductive organs, and thus differs from strobilization in tapeworms and certain jellyfish. Metamerism arises either from a bilateral series of coelomic pouches which form the segmental muscles, kidneys, and body cavities of lower forms, or from mesoblastic somites which form the skeletal and muscular segments of vertebrates. Repetitive features of the nervous system are acquired secondarily through the influence of mesodermal metameres upon adjoining ectodermal tissues. Several primitive embryonic somites become fused in the heads of adult arthropods and vertebrates. See Coelom, Muscular system, Neurulation

References in periodicals archive ?
Interior metameres together with the acron formed the gnathosomal region.
Antennae, palps, and initial metameres bearing parapodia often differentiate prior to metamorphic loss of the prototroch.
As mentioned, for some of our experiments, earthworms had their suprapharyngeal ganglia removed, which is accomplished by using a razor blade to cut a single midline incision into the dorsal surface from the earthworm's first metamere to its fourth metamere.