Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae).

A revision of the known Antarctic species of the genus Halecium has been carried out, based on the study of both type and non-type material. For each species a list of synonyms, a diagnosis, a broad description (with the exception of the recently described H. frigidum and H. exaggeratum), a discussion of its relationship with other members of the genus, and an account of its autecological data are given. Thirteen Antarctic species of the genus, including H. pseudodelicatulum sp. nov. and H. pseudoincertus sp. nov., are considered valid. Halecium tubatum is considered as species inquirenda. Halecium ovatum and H. macrocaulus are considered to be junior synonyms of H. interpolatum and H. incertus, respectively. The presence of H. delicatulum and H. tenellum in Antarctic waters is questioned. All Antarctic records found in the literature have been checked. The cnidome proved to be a useful tool for species identification in some cases. Finally, a general survey of the geographical and bathymetric distribution of the species is presented.