1. Terebella (Annelida, Terebelliformia) and Epistylis sp.1 (Ciliophora, Sessilida)

Most if not all specimens of Terebella sp. collected at Vellar estuary were severely infested with ciliate epibiont protozoans Epistylis sp.1 . The ciliates were found all over the worms’ bodies, on the buccal tentacles, lips, branchiae and dorsal and ventral body surfaces, but with clear preference for grooved regions on the body wall, such as between neuropodia and along the mid-ventral groove (Fig. 2A–C), possibly because these regions are more sheltered. Partially contracted individuals of Epistylis sp.1 are 52.56 µm long, in average, in 50 individuals measured, and were only found in solitary form (Fig. 2A–E), ~300–350 individuals per worm, in average, in 10 worms counted. Nevertheless, the tissues of the worm did not show lesions of any type at attachment points, suggesting that the ciliates are more likely ectocommensals, rather than parasites.