Abstract:Medusae play an important role in marine ecosystem.The species composition,Quantitative distribution and seasonal variation of Medusae in the Bohai Sea were determined in a discontinuous period from 1959 to 1997.There were totally 41 species,among which were 35 species of Hydrozoa,4 species of Scyphomedusae and 2 species of Ctenophore,respectively.Most species were found in relatively low salinity habitat,only a few in high salinity habitat for a very short time in each sampling year.The seasonal occurrence...