Phylogenetic analysis of the Hsp70 sequences reveals the monophyly of Metazoa and specific phylogenetic relationships between animals and fungi.

To understand the early evolution of the Metazoa, it is necessary to determine the correct phylogenetic status of diploblastic animals. Despite cladistic studies of morphological characters and recent molecular phylogenetic studies, it remains uncertain whether diploblasts are monophyletic or paraphyletic, and how the phyla of diploblasts are phylogenetically related. The heat shock protein 70 (Hsp70) sequences, because of their ubiquity and high degree of conservation, could provide a useful model for phylogenetic analysis. We have sequenced almost the entire nucleic acid sequence of cytoplasmic Hsp70 from eight diploblastic species. Our data support the monophyly of diploblastic animals. However, the phylogenetic relationships of the diploblast groups were not significantly resolved. Our phylogenetic trees also support the monophyly of Metazoa with high bootstrap values, indicating that animals form an extremely robust clade.