<P> Segmentation in biology is the division of some animal and plant body plans into a series of repetitive segments . This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida . These three groups form segments by using a "growth zone" to direct and define the segments . While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning . Even within these groups, different organisms have different mechanisms for segmenting the body . Segmentation of the body plan is important for allowing free movement and development of certain body parts . It also allows for regeneration in specific individuals . </P> <P> Segmentation is a difficult process to satisfactorily define . Many taxa (for instance the molluscs) have some form of serial repetition in their units, but are not conventionally thought of as segmented . Segmented animals are those considered to have organs that were repeated, or to have a body composed of self - similar units, but usually it is the parts of an organism that are referred to as being segmented . </P> <P> Segmentation in animals typically falls into three types, characteristic of different arthropods, vertebrates, and annelids . Arthropods such as the fruit fly form segments from a field of equivalent cells based on transcription factor gradients . Vertebrates like the zebrafish use oscillating gene expression to define segments known as somites . Annelids such as the leech use smaller blast cells budded off from large teloblast cells to define segments . </P> <P> Although Drosophila segmentation is not representative of the arthropod phylum in general, it is the most highly studied . Early screens to identify genes involved in cuticle development led to the discovery of a class of genes that was necessary for proper segmentation of the Drosophila embryo . </P>

What is an animal that has a segmented body