Cnidaria is a very interesting group, it's amazing how diverse it really is even though is an old lineage and hasn't changed that much since their appearance on planet Earth.

Those pictures are amazing, that water jelly and red-eyed medusa are gorgeous! But the one that caught my attention was the tailed jellies pic, it's the first time I see a colony like this one.

A very nice post :) I'd like to contribute with it: jellyfishes aren't a family, technically. Most of them are part of different classes inside Cnidaria, which is a phylum or major taxonomic group where jellyfishes, anemones and corals are placed. Each class is composed by lower taxa (like families, genera, species, sub-spicies...) and basically, it's a classification staircase :)

I hope it helps a little! Have a very nice weekend <3