Newly Observed Association from the Northern Adriatic Sea: Epizoic Ciliates and Scaled Polychaete Worms

Ciliate protozoans, particularly representatives of the subclass Peritrichia, are well known to establish epibiotic relationships with an array of aquatic Metazoans, nonetheless, very few studies regard these epibionts on polychaetes. In this research we report presence of ciliate peritrichs of the genus Cothurnia, likely to be C. amphicteis and C. peloscolicis, on scaled polychaetes Malmgrenia lilianae, M. andreapolis (fam. Polynoidae) and Sthenelais boa (fam. Sigalionidae), from the Northern Adriatic Sea (Mediterranean). Further morphological studies based on SEM microscopy will be done in order to confirm the identity of Cothurnia species found. This is the first record of the association between ciliates and polychaetes of the family Sigalionidae, and the first report of polychaete-ciliate association from the Adriatic Sea. Moreover, until today representatives of genus Cothurnia were reported from the Adriatic Sea only twice, as epibiont on algae and copepods in the Northern Adriatic. In our research, ciliates (from only few individuals to several tens per polychaete host) were found attached on scale worms chaete, sometimes more than one ciliate per chaeta. Chaetae seem to be favourable base for the attachment of sessile ciliates presumably because the water movement produced by the nearby positioned polychaete branchiae improves conditions for ciliates feeding. On the other hand, considering small size of ciliates, their position on chaete and low density on the host body, it is not very likely that ciliates have negative influence on polychaete host. However, detailed studies should be done in order to elucidate cost-benefit of each partner in this association. More than 21000 individuals from 230 polychaete species were carefully analysed from the same three stations in the northern Adriatic Sea from 2003 to 2008, nonetheless Cothurnia ciliates were only found on the three above mentioned polychaete species, suggesting that these host-symbiont relationships are highly specific. The lack of the previous records of ciliates on polychaetes in the Adriatic Sea probably reflects the lack of research efforts in that direction. This association might be much widespread phenomenon then currently known and it deserves more attention and further investigations.