The Hydromedusae of the Amsterdam Mid North Atlantic Plankton Expedition, 1980 (Coelenterata, Hydrozoa)

A faunistic description is given of the Hydromedusae collected during the 1980 Amsterdam Mid North Atlantic Plankton Expedition. In all, 30 species have been caught during the sampling period April 11-May 2, 1980. Remarks are made on structural details of some of the specimens collected. Latitudinal and vertical distribution patterns are given and data on the abundance of some species are recorded. For several bathypelagic species a faunal boundary is assessed at about 40°N, probably coinciding with the transition of eutrophic warm temperate water to oligotrophic Sargasso Sea water. This boundary is less sharp in the epi- and mesopelagic zones. Remarkable records are those of Calycopsis gara Petersen, 1957, Neoturris pileata (Forskål, 1775), Sibogita geometrica Maas, 1905, Tima flavilabris Eschscholtz, 1829, and Zygocanna vagans Bigelow, 1909.