Thevarietyofaquaticnonindigenousanimalsinmarinehabitatsworldwideincludesmorethan16planktonicCopepodaspecies.Acartiatonsaisaverysuccessfulone,distributedinmanyseas.ItsinvasionintoEuropeanseaswasanalyzedbefore(Brylinski,1981),butfromthattimeA.tonsaextendeditsrangeinEuropeanaquatichabitats.TheauthordescribesthehistoryoftheA.tonsainvasionintothePonto-Caspianbasinaswellassomemisleadingearlierpublications.MorphologicdifferencesbetweenA.clausiandA.tonsa,theneglectofwhichledtothewrongidentification,wereexamined.ThedataonA.tonsaandtotalcopepoddynamicsintheSevastopolBayduringtheperiodof1976~1996andthesamedataontheCaspianSeasince1981wereanalyzed.TheaveragesizeofA.tonsainnewhabitatsdecreased,anditsrelativedensityintheBlackandCaspianSeasgraduallyincreased.
