Urmetazoan
（重定向自Gastraea）
![Maximum Likelihood Phylogenetic Tree of Metazoan Relationships](/Images/godic/202501/14/Metazoan_Phylogenetic_Tree1321.png")
The Urmetazoan is the hypothetical last common ancestor of all animals. It was undoubtedly marine, but beyond this its form is difficult to determine; five different hypotheses have been put forward, and discriminating between them is difficult because the relationships of animal phyla are not completely resolved.