Abstract: The phylogenetic relationships of 9 superfamilies of Hydrachnellae (=Hydrachnidia)were studied.The cladistic analyses were made using 23 morphological characters and 3 biological characters.A classification scheme,based on the phylogenetic relationships within Hydrachnellae,is proposed for 5 groups with 9 superfamilies.Pseudohydrachnidia is the most primitive group containing one superfamily (Stygothrombioidea);Protohydrachnidia contains one superfamily(Hydrovolzioidea);Euhydrachnidia consists of 2 groups Achihydrachnidia and Neohydrachnidia;the Achihydrachnidia contains three superfamilies(Hydrachnoidea,Hydraphantoidea,Eylaoidea)and Neohydrachnidia four superfamilies(Sperchontoidea,Lebertioidea,Hygrobatoidea,Arrenuroidea).Following sister groups are suggested:Pseudohydrachnidia and Protohydrachnidia+Euhydrachnidia;Protohydrachnidia and Euhydrachnidia(Achihydrachnidia+Neohydrachnidia);Achihydrachnidia and Neohydrachnidia.Comparisons with hypotheses by other authors are given.

Key words: Hydrachnellae, superfamily, cladistics, phylogeny