What is pseudometamerism?

Metamerism is the phenomenon of occurrence of many, structurally similar segments in the body of an animal. However, all segments could not be exactly alike as some of them are specialised to perform different functions. Each body segment is called metamere.  Earthworm is a classic example of metameric animals.
Metamerism can be of two types: true metamerism and pseudometamerism.
In true metamerism, segmentation is both  externally and internally and all the segments work together. In pseudometamerism, either the segmentation is only external or the segments behave independently not as a unit, or both. Example, tapeworm.