It is not quite clear that how and why
metamerism has evolved or how were the ancestors benefited by it. But it is
possible that metamerism/segmentation initiated from the musculature of
elongated swimming worms. Due to segmentation the body gets divided into
metamere which facilitates in swimming. Metamerism has helped in locomotion in
many ways. The co-ordination of muscle contraction and the fluid filled
coelomic cavity makes swimming and locomotion movement more efficient and it is
more advanced over ciliary or creeping movement found in lower invertebrates.
The fluid filled
coelomic cavities serves as a hydrostatic skeleton which helps in burrowing.
Precised movement also occurs by differentiated turgor affected by the flow of
body fluid from one part of the body to other.
Another advantage of metamerism or segmentation
is that it provides opportunity to different segments to specialize it for
different function. Thus it leads to rapid evolution of high grade of
organisation. This is not clearly marked in annelids but it is well developed
in arthropods. Metamerism has greatly contributed toward the greater complexity
of animal body and higher grade of organisation in animals. Thus, some
indication of primitiveness of an animal can be determined by the degree of
segmentation it displays.
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