MUIRHEAD'S ,MYSTERIES: Freshwater jellyfish

I found the following on a web site titled A Small Jellyfish conquers the world https://www.aqualog.de/en/blog-en/a-small-jellyfish-conquers-the-world/ "The freshwater jellyfish was first seen in Europe in 1880, at Regent´s Park in London, where this delicate creature, which attains a diameter of only some 2 cm, turned up in a tank housing tropical water lilies. At that time there was far more interest in animals than there is today, and the freshwater jellyfish hit the headlines worldwide. This, the first and only freshwater jellyfish then known, was scientifically described in the same year as it was discovered – twice! – as Craspedacusta sowerbii LANKESTER, 1880 andLimnocodium victoriaALLMANN, 1880. The first name was published somewhat earlier and hence is valid. So the scientific name of the freshwater jellyfish is Craspedacusta sowerbii.

Detective work
But where did this creature appear from so suddenly? It was already known that jellyfishes are no more than the sexually reproductive stage of a polyp. Jellyfishes belong to the phylum Cnidaria and their closest relatives are the sea anemones and corals. Hence the normal habitus of a jellyfish looks like a small sea anemone. This can perhaps best be compared with toadstools and mushrooms. The normal state of these fungi is a network of filaments that live underground. The parts that appear above ground and can be made into tasty dishes (as long as they aren’t poisonous fungi) are only the fruiting bodies, not the fungus itself..".