Really huge, neutral buoyancy creatures living in Jupiter. One is attracted to an event at much higher "altitude" but is attacked by... well lets call them Jovian sharks. The creature can disassemble and reintegrate if necessary - something like that.
I think a manned mission to Jupiter that gets in trouble is a major element of the plot, but I mostly just remember bits about the Jovian life forms.
I'm pretty sure this is a well known story and author - I just can't place it. Don't have access to my books right now either :(