A deep-sea hydrothermal vent community dominated by Stauromedusae

A dense population of stauromedusan scyphozoans (morphologically similar to previously described species within the genus Lucernaria) was encountered in a previously undocumented area of hydrothermal activity along the crest of the East Pacific Rise (Lat. 20°50.304′N; Long. 109°05.422′W; depth of 2605 m). A few galatheid (Munidopsis subsquamosa) and bythograeid (Bythograea thermydron) crabs and occasional anemones (Cyananthea sp.) were the only other vent-associated megafauna observed within the region. This report represents: (1) the first documented occurrence of a biological community dominated by Stauromedusae at an active hydrothermal vent; (2) one of the deepest reported occurrences of Stauromedusae in the world’s oceans; and (3) documentation of the existence of a species within a class (Scyphozoa) of organisms that thus far has not been reported from hydrothermal vents or other reducing environments.