Taxonomy uses taxonomic units, known as "taxa" (singular "taxon"). This genus is thus regarded as an entrenched paraphyletic wastebasket taxon. The genus thus functioned as a typical "wastebasket taxon". No subspecies of this taxon are known. Each of these terms describes a valid taxon, phylum, subphylum or family. Genome duplication occurred prior to the divergence of this taxon. Others consider them a sister group of vertebrates in the common taxon of craniata. Others consider them a sister group of vertebrates in the common taxon of Craniata. Lepospondyli is a diverse taxon of reptiliomorph tetrapods. Classification of members of this taxon is infrequently based on their antigenic properties. Another group of organisms that belong in this taxon are the corallicolids. However, other extinct groups fall within some circumscriptions of this taxon. Autopolyploids are polyploids with multiple chromosome sets derived from a single taxon. The sister taxon is the subclass Dictyostelia. This is the principle that the name of each taxon must be unique.