Boule-like genes regulate male and female gametogenesis in the flatworm Macrostomum lignano

► The function of boule genes is shown for the first time in a lophotrochozoan. ► There are three distinct macbol orthologues in the flatworm Macrostomum lignano. ► Macbol1 and macbol2 are testis-specific, macbol3 is essential for oogenesis. ► RNAi arrests male meiosis (macbol1) and impedes egg maturation (macbol3). ► Macbol1 is able to rescue meiotic divisions in boule-mutant Drosophila melanogaster.