Jellyfish in the Oceanium Rotterdam Holland

I think they look like U.F.O's or aliens from outer space, but here is a description
Since jellyfish are not actually fish, some people consider the term jellyfish a misnomer,
and American public aquariums have popularized use of the terms jellies or sea jellies instead.
In its broadest sense, the term jellyfish also generally refers to members of the phylum Ctenophora.
Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores,
are generally transparent or translucent, and exist in shallow to deep portions of all the world's oceans.
The original Rotterdam zoo was lost in the bombing of Rotterdam in World War II, which destroyed most of the city centre.
Some streetnames, such as Diergaardesingel (Zoolane), still recall the old zoo. Blijdorp was rebuilt slightly to the north,
where it opened to the public in its current location on December 7, 1940.
The new zoo was designed by Dutch architect Sybold van Ravesteyn, who designed the central railway station in Rotterdam, as well. In 2001, 'Blijdorp' became almost twice as large when it opened a new western part, called Oceanium, with its main attraction an aquarium. In April 2004,
the whole zoo was declared a national monument.