 In the past, some zoologists grouped bilaterian animal phyla based on characteristics related to the coelom for practical purposes, knowing, and explicitly stating, that these groups were "not" phylogenetically related.Animals were classified in three informal groups according to the type of body cavity they possess, in a non-taxonomic, utilitarian way, as the Acoelomata, Pseudocoelomata, and Coelomata.These groups were never intended to represent related animals, or a sequence of evolutionary traits.