Overview of all steps leading to the final release of the dataset: 1 sampling, independently performed at the three different institutions (AUTH = Aristotle University of Thessaloniki,  UNIPA = University of Palermo, HCMR = Hellenic Centre for Marine Research) 2 identification of polychaete specimens in the laboratory 3 data in paper-based format 4 digitisation 5 data in electronic format (spreadsheets) 6 integration of the three independent datasets into a standardised format, exclusion of records not identified to species level, retrieval of missing information, georeferencing of coordinates through Google Maps, standardisation of taxonomy against the World Register of Marine Species and recent literature, general quality control 7 export of data as a DarwinCore Archive 8 generation of dataset-level metadata 9 publication of the data as a data paper and through an IPT server 10 in the future, further dissemination of data by integration into other databases, personal downloads, archiving, etc.