The relationship between the different animal groups has been a puzzling question for scientists for more than a decade and we do not know if we ever will obtain the correct answer. However, our methods to propose consistent theories about the animal evolution and relationships are always being improved and today many scientists try to combine information from molecules (RNA and DNA) and morphology. The tree below shows one hypothesis about the animal phylogeny and the position of Gnathifera. The tree is a combination of some of the most recent phylogenetic analyses, but to simplify it several groups have been left out and others have been united in very large superphyla. The first group to branch off is the Deuterostomia, which, i. e., contain the vertebrates and the echinoderms. After Deuterostomia, the Ecdysozoa branch off. Ecdysozoa are a group with animals that molt their cuticle during growth and contains phyla such as Arthropoda, Tardigrada and Nematoda. The next group to branch off is the Trochozoa, which contain well-known groups like the annelids and the mollusks. The three remaining groups are together referred to as the Platyzoa, and we see that inside Platyzoa, Gnathifera is sister group to Gastrotricha and Platyhelminthes (the flatworms).