Student or Learner
The jellyfish live / lives in the water.
Which verb should I use? I believe the verb should be 'live' but wonder whether 'The jellyfish' can refer to one jellyfish in the above sentence.
However, if you want to refer to the general category, then I suggest either
"The jellyfish lives" or
but not "The jellyfish live."
Like "The horse is a useful animal" or "Horses are useful animals" but not "The horses are useful animals" -- if you are talking about horses overall.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.