Soft-bottom hydroids (Cnidaria: Hydrozoa) collected in the Ría de Vigo (NW Spain)

Thirty-one hydroids species, living on the sublittoral soft-bottoms, are reported from the Ría de Vigo, representing one third of the species currently known, from the Ría. Twenty-four are Leptomedusae and only seven are Anthomedusae. The identifications of Campomma hincksi, Cosmetira pilosella and Laodicea undulata, based only on the hydroid stage, are discussed. The report includes one species that could be identified only to generic level as well, and also a description of the previously unknown male gonotheca of Halecium liouvillei. Five species, Merona cornucopiae, Hydractinia echinata, Lovenella clausa, Opercularella spec, and Laomedea angulata, were collected exclusively from soft bottoms that seem to be their typical habitat. Analysis of geographical distribution shows that the cosmopolitan species are dominant followed by tropical-Atlantic and boreal groups; and Indo-Pacific and endemic species are absent. Concerning life cycles 60% of the species have fixed gonophores. The species with free medusae (40%) dominate only in the cosmopolitan group.