I collected this strain in spring 2021 in Helsinki and have kept them going ever since. I suspect them to be Daphnia pulex. Their adult size is around 2mm, so they're smaller than Daphnia magna but bigger than Moina.
For me, this has been very easy strain of Daphnia to keep in captivity. Easiest way is to just put them outdoors in sunlight, but they can also be cultured indoors under strong daylight lamp.
Package includes a breathing bag with several scoops of live individuals.