Summary On investigation of a dense population of mud tube building polychaetes tentatively identified as Polydora ciliata it was found that many individuals also showed morphological characteristics more usually associated with other members of the same genus. This prompted the examination of the morphology of P. ciliata from a number of different areas with the aim of assessing the stability of some of the characters used in the taxonomy of its genus. These proved to be highly variable, did not group together consistently and overlapped with some of those of P. limicola (Annenkova) and P. ligni Webster. No clear distinction between P. ciliata and P. limicola could be made on the grounds of the characteristics examined but the overlap between P. ciliata and P. ligni was small.
Many papers dealing with nonindigenous species in the Black Sea do not mention the polychaete Polydora limicola Annenkova, a new invader in the Pontic-Azov Basin. In this connection, we will analyze here the taxonomic status of this species and discuss the history of its introduction and distribution in the northwestern Black Sea and related coastal lagoons. It is shown that P. limicola is now one of the most common species of the benthos in the Black Sea, especially in estuarine areas and coastal lagoons. The naturalization of this species resulted in changes in the structure of some bottom biocenoses of this region.
Recent sequencing of ctenophore genomes opens a new era in the study of this unique and phylogenetically distant group. The presence of neurodevelopmental genes, pre- and postsynaptic modules, and transmitter molecules is consistent with a single origin of neurons.