ORFans in mitochondrial genomes of marine polychaete Polydora

In this study, we conducted sequencing and analysis of the mitochondrial genome of Polydora cf. ciliata, a polychaete worm, part of whose life cycle takes place in low-oxygen conditions. Within the mitochondrial genome of Polydora cf. ciliata, we discovered three unique "ORFan" regions with no resemblance to standard metazoan mtDNA genes. Our analysis of these ORFan regions suggests that they likely encode functional proteins, and possibly originated when the Polydora/Bocardiella species complex separated from the rest of the Spionidae. Furthermore, through RNA sequencing, we identified that two of these ORFan regions are actively transcribed, while the third region produces stable mRNA only partially.