Runnig Tittle: Syllidae-Protozoan epibiosis Corresponding author:
[email protected] The tag-along friendship: epibiotic protozoans and syllid polychaetes. Implications for the taxonomy of Syllidae (Annelida), and description of three new species of Rhabdostyla and Cothurnia (Ciliophora, Peritrichia). Álvarez-Campos, Patricia1*, Gregorio Fernández-Leborans2, Aida Verdes3, Guillermo San Martín1, Daniel Martin4, & Ana Riesgo5 1 Departamento de Biología (Zoología), Universidad Autónoma de Madrid, Facultad de Ciencias, Cantoblanco 28049, Madrid, Spain. 2 Departamento de Zoología, Universidad Complutense de Madrid, Facultad de Biología, C/ José Antonio Novais, 12, 28040, Madrid, Spain 3 Department of Natural Sciences, City University of New York, Baruch College, 55 Lexington Avenue, New York 10010 NY, USA 4 Department d’Ecologia Marina, Centre d‘Estudis Avançats de Blanes, CEAB-CSIC, c/ Accés a la cala St Francesc, 14, 17300, Blanes, Spain 5 Departamento de Biología Animal, Facultad de Biología, Universitat de Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain. Abstract The presence of peritrich ciliate epibionts Rhabdostyla sp. and Cothurnia sp. on Syllidae polychaetes is reported here for the first time, including the description of three new species of epibiont ciliates. The protozoans were mainly found at intersegmental furrows, close to parapodial bases of newly collected specimens of Syllis magdalena, Syllis sp., Salvatoria sp. and Salvatoria concinna n. comb. from Chile, Syllis prolifera from Spain and Prosphaerosyllis magnoculata from New Zealand. In addition, epibiont protozoans were found on the dorsal surface, nuchal organs, mouth opening and anterior cirri of Syllis elongata from Peru, and the ventral surface of Typosyllis macropectinans from Australia. The discovery of protozoan epibionts on syllid polychaetes has important taxonomic implications that are discussed here.