ABSTRACT. – Information from 40 harbours was used to investigate the diversity and habitat affinities of Ophryotrocha species living in Central Mediterranean coastal habitats. Three environmental descriptors were considered: climate, boat traffic in harbours and fouling assemblages of port wharfs. Moreover, the diet was studied through the analysis of faecal pellets. The number of Ophryotrocha species did not vary among the climatic sub-areas, while the main, high traffic harbours exhibited a higher number of species with respect to the minor harbours. Ophryotrocha species can colonise all the fouling types considered, but the highest number of species was observed in mixed, heterogeneous assemblages. In most of the places investigated, two or more species co-existed on both harbour and wharf scales. The three most common species, O. labronica, O. puerilis (Mediterranean indigenous) and O. japonica (a non-indigenous species), differed in their affinities for climatic areas and harbour typology, but no significant preferences were observed with respect to the fouling types. The examination of faecal pellets from animals collected in the field suggested that all the species are omnivorous. Ophryotrocha species can live in very different types of harbour habitats. However, the ability to successfully colonise these environments varied strongly among species, perhaps because of their “history” (especially in the case of non-indigenous species), tolerance and habitat preferences/requirements.