Question

what is meant by metamerism

Answer 1

In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. In animals, metameric segments are referred to as somites or metameres. 

Answer 2

the condition of having or the stage of evolutionary development characterized by a body made up of metamers that is usually held to be an essential prelude to the differentiation of the more highly organized animals (as arthropods and vertebrates) through the disproportionate development and elaboration of some segments together with the coalescence, reduction, or loss of others