Question

Define metamerism.

Answer 1

The word metamerism can be broken down into two and it can be defined accordingly by combining the meaning of two words. The word metamerism should not be confused with the word segmentation.

Complete answer:
Meta: One behind the other. Merism: Repetition of similar parts. The phenomenon of having linear series of body segments fundamentally similar in structure but not all the structures are similar completely because they carry out special functions. In organisms, the metameric segments are called somites or metameres.

Metamerism is an event that happens in the mesoderm resulting in the repeated units of ectoderm and mesoderm products and the endoderm is not involved in it. There are two types of metamerism namely,

Homonymous metamerism: It is further divided into true metamerism and pseudometamerism.
• True metamerism is seen in earthworms where in each segment the repetition of the organs and tissues can be found.
• Pseudometamerism is seen in tapeworm and composed of many repetitive segments for reproduction and nutrient exchange.
• The difference in the metamerism between tapeworm and earthworm is that the segments in earthworm work together for the whole organism but in tapeworm it works separately.

Heteronomous metamerism:
• It is a condition where the metameres have joined together to form the same functions. Insects are a very good example for it which has five metameres in the head, three in thorax, and around 11 in the abdomen.

Additional information:
The event that results in the grouping of metameres is called tagmatization and each group is referred to as a tagma. In plants metamerism is seen and they are called phytomers.

Note: Segmentation shouldn’t be confused with metamerism as metamerism is a product of mesodermal events and segmentation is ectodermal derived.
In chemistry, the phenomenon of compounds having the same molecular formula but different number of carbon atoms on either side of the functional groups is called metamerism.