Referee 1's Review:

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N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication, the manuscript has been revised in light of these comments and to address other editorial requirements.
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This is an interesting article that provides two major results: 1- A detailed phylogenetic analysis based on a large number of molecular markers of the different groups of unicellular eukaryotes (collectively referred as the Choanozoa) related to the animals, and 2- The identification in Choanozoa members of homologues of several proteins involved in signaling and cell adhesion that were thought to be exclusive of animals. These are very important results that deserve publication.

The only important remark is that authors should check the Table 1, it is empty in the PDF version submitted to the Plos site.

In addition, I have only a few minor suggestions that can improve the clarity of the manuscript. In particular, I think that it would be useful to divide the Results and Discussion into different sub-sections, for example a first one for the phylogenetic analysis and a second one for the detection of signaling and cell adhesion protein homologues in Choanozoa.

Finally, the short paragraph about the taxonomic description of the novel Class Filasterea should be placed at the end of the main text.