Segmentation: Dividing the body into parts is called segmentation. Segmentation is of two types:
(i) Superficial segmentation: In this type of segmentation the animal appears segmented only from outside, but is not divided from inside. This kind of segmentation is found in coelenterate and some other pseudocoelomate animals.
(ii) Metameric segmentation: In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs. For example, in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is known as metamerism. This type of segmentation is found in Annelida, Arthropoda and vertebrates.