Diurnal vertical migration of Solmissus albescens (Hydromedusae) in the Southern Adriatic

During a study on diurnal vertical migration in the hydromedusa Solmissus albescens (Gegenbaur, 1856), 112 net samples were taken from a depth of 1000 m to the surface. Sampling was performed in July, August, and September, 1969, at a station located 20 miles SSW of Dubrovnik (Yugoslavia). S. albescens migrates vertical distances of over 300 m. No significant influences on migration were noticed due to environmental factors (temperature, salinity, vertical water currents, etc.). The hydromedusa was able to approach surface layers. The recording obtained at various water-depth levels are considered in relation to illumination, mechanisms of evolution, and feeding of S. albescens.