Interestingly, a putative ccdc151 ortholog (amino acid similarity 56%; identity 33%) is also required for proper cilia function in planarians (Figure S4). Planarians are flatworms that move on a ventral ciliated epithelium (Figures S4A–S4A′) and defects in cilia function cause characteristic locomotion defects.57 Hence, planarian locomotion represents a simple readout for cilia dysfunction. We found that ccdc151 RNAi-treated planarians (Figure S4C) had severely reduced locomotive ability, moving only by contracting their muscles rather than gliding (Figures S4D–S4D′; Movies S5 and S6). TEM analysis revealed a loss of ODAs in the mutant axonemes compared to control axonemes, consistent with the findings in zebrafish and mouse CCDC151 mutants (Figure S4E). Together, these data support an evolutionarily conserved role for ccdc151 in establishing proper ciliary motility in vertebrates and invertebrates.