Phylum
Phylum Phylum, in biology , major category, or taxon, of organisms with a common design or organization. This design is shared by all members of the phylum, even though structural details may differ greatly because of evolution . The assumption is made by biologists that all members of a phylum have a common ancestry. A phylum is part of the hierarchy of classification of organisms. It is an arbitrary grouping; that is, it is developed from a combination of scientific observation, theorizing, and guesswork in an attempt to find order in the complexity of living and extinct life forms. The same is true of all classification levels above and below it except for species, which consist of organisms known to be capable, at least potentially, of interbreeding (see Species and Speciation ). related topics: animal phyla plant phyla