Polyzoa is back: The effect of complete gene sets on the placement of Ectoprocta and Entoprocta

Abstract

The phylogenomic approach has largely resolved metazoan phylogeny and improved our knowledge of animal evolution based on morphology, paleontology, and embryology. Nevertheless, the placement of two major lophotrochozoan phyla, Entoprocta (Kamptozoa) and Ectoprocta (Bryozoa), remains highly controversial: Originally considered as a single group named Polyzoa (Bryozoa), they were separated on the basis of morphology. So far, each new study of lophotrochozoan evolution has still consistently proposed different phylogenetic positions for these groups. Here, we reinvestigated the placement of Entoprocta and Ectoprocta using highly complete datasets with rigorous contamination removal. Our results from maximum likelihood, Bayesian, and coalescent analyses strongly support the topology in which Entoprocta and Bryozoa form a distinct clade, placed as a sister group to all other lophotrochozoan clades: Annelida, Mollusca, Brachiopoda, Phoronida, and Nemertea. Our study favors the evolutionary scenario where Entoprocta, Cycliophora, and Bryozoa constitute one of the earliest branches among Lophotrochozoa and thus supports the Polyzoa hypothesis.