This study reviews all European hydrozoan species belonging to the capitate families Acaulidae, Boreohydridae, Candelabridae, Cladocorynidae, Cladonematidae, Margelopsidae, Pennariidae, Protohydridae, and Tricyclusidae. Updated diagnoses for the families and genera are provided and existing taxonomic problems solved or at least outlined. Candelabrum verrucosum Bonnevie, 1898 is regarded as a valid species and redescribed based on a new record from Greenland. Although Spadix purpurea Gosse, 1853 may be a senior synonym of Candelabrum cocksii (Cocks, 1854), the latter is regarded as the valid name, this because the former name has not been used after 1899, while the latter has been widely used (ICZN article 23.9.1.1). Likewise, two senior synonyms of Eleutheria claparedii Hartlaub, 1898 are declared as invalid as they have never been used since their original introduction by Haeckel.
