What is metamerism? Compare the metamerism we see in earthworms to what we see in arthropods. What are the commonalities and differences?

1. Metamerism is a phenomenon that appears in some animals and it refers to linear disposition of their body segments that are similar in structures. These body segments are called metamers or somites and they include only the ectoderm and mesoderm (not endoderm). Metamers repeat serial and they have role in advanced locomotion. Metamerism might be homonymous when its strict or heteronymous when units are grouped together to perform similar functions.

2. Earthworm is an example of homonymous metamerism, meaning that its segments are strict. The subtype of homonymous metamerism in which Earthworm belongs is called true metamerism because in each its segment there is a repetition of organs and muscles. On the other hand, Arthropods are example of heteronymous metamerism when units are grouped together to perform similar functions. So, they have for example, head (5 metameres), thorax (3 metameres), and abdomen (11 metameres).

3. Similarities between Earthworm and Arthropods' metamerism are:

• Metamers are similar in structure

• Each metamer has its function

• Involved in locomotion

Differences is that metamers in Earthworm all work together for the whole organism while in Arthropods they are functionally separated in groups with different functions.