The Author, when examining a population of Archiannelids found in the littoral benthic mesopsammal of the Gulf of Catania, which seemed to belong to the species Mesonerilla intermedia Wilke, remarked the existence of some noteworthy morphologic differences among the various individuals. Such differences concerned especially the number and length of the antennae and the presence or lack of bristles on the oral segment. However, by rearing such individuals, the Author remarked that after some days all of them were furnished with bristles on the oral segment and with three well developed antennae. On the basis of these results, the validity is questioned of a group of species assigned to the genus Mesonerilla, i.e. M. roscovita, M. fagei and M. biantennata, whose distinction based just on the number and length of the antennae and on the presence or lack of bristles on the oral segment.