TRUE METAMERISM

When the segmentation of the mesoderm occurs then the Metamerism occurs. It commonly occurs in the annelids, arthropods, and chordates. Annelids body contains a number of segments. One interesting point is that the number of segments remains constant in all the animals of a particular species. The addition of segments stops in these animals as the animal becomes mature. Arthropods are having the internal metamerism, while on the other side Annelids possess external metamerism. If the metamerism is shown completely and shown in all the systems then it is called a complete metamerism.
 
PSEUDO METAMERISM

A perfect example of the Pseudo Metamerism is tapeworms. In this type of the metamerism, The segmentation of the ectoderm is the main and the base cause of the metamerism. Animals with these type of metamerism are having the different numbers of the segments in the same species. As well as the addition of the new segments continues throughout the whole life of the animal. The segments are different in the shapes as well. Their degree of the development is different as well. This kind of animals are having the zero cooperation between their segments and the segments are formed at the anterior end of their body.