Recent studies have revealed that changes of key genetic toolkit at cellular and developmental level can generate novel characters in morphological structures. To better understand, it we need to dig into the evolutionary history of these critical genes. Considering that DNA sequences are more vulnerable and variable to selection pressure during long evolutionary history, we used KHDRBS protein sequences of major metazoan taxa for later analyses. We acquired multiple KHDRBS protein sequences mainly from NCBI and Ensembl. These sequences were aligned by ClustalW algorithm for next phylogeny analyses. We constructed phylogenetic trees by MrBayes (Figure 1A) and ML methods (Figure 1B). These two phylogenetic trees were generally consistent with each other. The analyses revealed that KHDRBS was traced back to Trichoplax adhaerens and Hydra vulgaris, the basal metazoans.