Tree derived from phylogenetic analysis of cyclin family proteins in H. sapiens , N. vectensis , T. adhaerens , A. queenslandica , M. brevicollis , and S. rosetta . Maximum likelihood (ML) and Bayesian analyses were conducted using RAxML and PHYLOBAYES 3.3, respectively. Both methods produced trees with nearly identical topologies. The first numbers above branches indicate Bayesian posterior probabilities (only key branches are labeled), and the second numbers above branches indicate ML bootstrap percentages. The scale bar shows the number of substitutions per site. Sequences of Hsa-Cables1 and Hsa-Cables2 were used as outgroups. All proteins are labeled with their accession numbers preceded by their species names. Species abbreviations are as follows: Hsa, H. sapiens; Nve, N. vectensis; Tad, T. adhaerens; Aqe, A. queenslandica; MBr, M. brevicollis. The alignment used for this analysis is found in Additional file 1: File S3.