Addendum to previous comment: I am reminded of Leviathans of Jupiter by Ben Bova(we lost him to covid pneumonia and stroke on 29 nov 2020)
The Leviathans..city sized sentient whale like creatures that replicate by splitting themselves ..a process called ‘budding’. A very enjoyable read. This thread made me look it up to read again. If you like good old fashioned sci-fi, I recommend it. It’s part of Ben Bova’s Grand Tour series.
Also led me to this interesting article on the Basking shark which has an absolutely gigantic mouth for filter feeding plankton.
https://www.nhm.ac.uk/discover/basking-shark-cetorhinus-maxi...