Representative species of the groups within Hydrozoa that were the object of study of HYPNO (from left to right and top to bottom): Amphinema rugosum (Anthoathecata), Mitrocomella polydiademata (Leptothecata), Lensia conoidea (Siphonophorae Calycophorae), Agalma elegans (Siphonophorae Physonectae), Botrynema ellinorae (Trachymedusae), Bathykorus bouilloni (Narcomedusae). Pictures: Luis Martell and Aino Hosia.