18. {Habitat fresh water{223} 56 {Habitat marine 22 {Megascleres include cladotyles _Acarnus_ {Megascleres include dumb-bell or sausage-shaped spicules forming { the main reticulum _Plocamia_ {Microscleres include bipocilli 20 19. {Microscleres include diancistra _Hamacantha_ {Megascleres include forceps _Forcepia_ {Skeleton formed of isolated monactines vertically placed { _Hymeraphia_ {None of the above peculiarities present 21 20. {Skeleton fibre not echinated _Iophon_ {Skeleton fibre echinated _Pocillon_ 21. {Skeleton with echinating spicules 28 {Skeleton without echinating spicules 30 22. {Spongin abundant 23 {Spongin scanty 25 23. {Fibre not echinated 24 {Fibre echinated _Diplodemia_ 24. {Fibre with a single axial series of spicules _Chalina_ {Fibres with numerous spicules arranged polyserially _Pachychalina_ 25. {Microscleres absent 26 {Microscleres sigmata and/or toxa 27 26. {Skeleton confused _Halichondria_ {Skeleton reticulate _Reniera_ {Rind and fistulous appendages present; microscleres sigmata 27. { _Oceanapia_ {No rind; skeleton reticulate; microscleres sigmata and/or toxa { _Gellius_ {Skeleton confused or formed of bundles of spicules with { echinating spined styles 29 28. {Skeleton fibrous or reticulate, or formed of short columns 45 {Skeleton formed of a dense central axis, and columns radiating { from it to the surface 52 {Spicules of the ectosome styles _Pytheas_ 29. {Spicules of the ectosome oxeas or absent _Clathrissa_ {Main skeleton confused. Special ectosomal skeleton absent { _Spanioplon_