| Summary: | The benthic hydroids collected on five lusitanian seamounts (Seine, Ampère, Lion, Gorringe, Josephine and Galice bank) during the French “SEAMOUNT 1” cruise, and those collected on the Great Meteor bank during the German “METEOR 42/3” cruise were studied. Global hydroid diversity account for 67 species included in 15 families. The most specious were Lafoeidae (12 species), followed by Campanulariidae, Plumulariidae and Sertulariidae (9 species), Aglaopheniidae and Haleciidae (6 species), Halopterididae (4 species) and Tiarannidae (3 species). The other families were represented only by one or two species. The highest species richness was recorded in Ampère (39 species) and Gorringe (38 species) seamounts, whereas intermediate values were recorded at the Great Meteor bank (22 species) and the lowest values corresponded to seamounts Josephine (12 species), Galice (9 species) and Seine (8 species). All the Lusitanian seamounts are located near continental masses and virtually all species are also reported from the shelf and slope of western Iberian Peninsula and Northwest Africa. Only one species Pseudoplumaria sabinae Ramil & Vervoort, 1992, seems endemic from Gorringe and Ampère banks and was not found elsewhere. The Great Meteor bank is a more oceanic seamount, quite distant from lusitanian seamounts and from the continents, but 16 of 22 species collected (73%) there were shared with those found in lusitanian seamounts. Among the remainder six species, four of them (Bedotella armata, Diphasia nigra, Nemertesia ventriculiformis and Symplectoscyphus bathyalis) are widely distributed in the Eastern Atlantic despite they were not collected in the other seamounts; Nemertesia belini were only reported from the Azores and Cape Verde Islands and one unidentified Halecium species was previously collected only from Lucky Strike hydrothermal field, in the Mid-Atlantic ridge (Calder and Vervoort, 1998). Therefore, the hydroid fauna from the Great Meteor bank is not significantly different from that of Lusitanian ...
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