There was a book a long time ago that I once read. It was beautiful, but what I remember most was a description of a fictional alien race of this giant mind that was made of solar systems or dark space clouds. There was another race that looked like jellyfish and it said most are doctors, in some science fiction book.
Possibly Barlowe's Guide to Extraterrestrials which is readable and downloadable at the link.
The book contains images of different alien races from dozens of various science fiction books.
Included in this is the alien Black Cloud from Fred Hoyle's story The Black Cloud. The Cloud is an intelligent interstellar hydrogen cloud 150 million kilometers in diameter.
However it was not a jellyfish like race that were doctors but Cinnrusskins who are an insectoid race from the books Hospital Station and Star Surgeon by James White.
Sounds like Barlowe's Guide to Extraterrestials - Which includes both the Medusa, a gas giant dwelling Jellyfish critter and Solaris, a ocean-like world mind, and the Black clouds, intelligent space clouds.