Water Worlds, probability and life
I have had similar thoughts as yours, specially for the case of a Europa or Enceladus type world, which is starting to seem the most likely type of planets for having liquid water. Think our Solar System, there is one Planet with liquid water on surface, one which had in past (Mars), however undersea oceans are almost certain in Enceladus and Europa and possible in several other bodies Ganymede, Callisto, Ceres, Titan and probably others. The lack of Sun light would certainly hinder development of life but I don't think it could be discarded. The aparent significantly higher probability of planets with water available in underground oceans migh somewhat compensate the less likely formation of life because of missing sunlight.
It is interesting the other answer that mentions that more advanced lifeforms having developed on land inspite of it being much later than ocean life, not sure if that could be extrapolated to other worlds since I wouldn't be sure why that has happened. Ocean life certainly is not in bad shape and there are probably more species at sea that at land. Just seems that the stage they have evolved is in most cases sufficient for survival in that environment without having needed to develop into intelligent beings.
Alien Ocean civilizations
I would make a difference between an ocean civilization in an ocean in contact with an atmosphere vs one under a layer of ice. 258
In the first case the civilization would eventualy reach the surface, and investigate the exterior, how much it could initially learn might depend on how deep they originaly evolved and presence or not of significant cloud cover in the atmosphere.
Under Ice Ocean Civs Some of what applies in this case probably aplies also to previous case if the civilization where deep enough to make light absent.
In these Europa-type worlds:
* There would be no sunlight anywhere.
* Therefore vision might not evolve or only in species evolving simultaneously some type of bioluminiscence, competing with other systems as sonar smell or others to interact with the world.
* Lack of light and vision would make astronomy unknown for long stages of civilization development.
* Maybe even the absence of paterns found in astronomy might slightly slow develoment of math vs other sciences.
A civilization as we know would probably be sedentarious, this would make it unlikely at first to develop among species living in the open ocean, I speculate if such civilization apeared it would be either at the sea floor on at the sea top, in contact with the ice cover. Current speculation on posibility of hot vents in Europa at the sea floor might make a bottom civilization seem more likely, but maybe a "Top" civilization would be possible too if the life mass is enough for large animals living far from rocky bottom (or maybe the top could be chemically active in some way too.)
Things in our evolution that we take for granted might take a different course of events, even knowing the world is round would probably not be known until the civilization expands enough to reach itself on the other end.
For all this civilization knows they would just as likely think that the ceiling extends indefinately, something that would be possible to continue believing even well after they knew the world was round and therefore that the floor is finite and their world has a "center".
I think this civilization would probably need to be at least at tech levels similar to ours or at minimum mid 20th century levels to even start speculating of the posibility of the world having an outer limit. This knowledge would probably be obtained from theoretical models, probably modeling pressures and gravitation. Gravitation, and <PERSON> laws in general would probably take much longer to be accurately undestood, as on Earth these where modeled with important inputs from astronomy and observation of planets. Other chances are detecting the Sun by some type of radiation penetrating the ice and ocean in levels detectable to some science instrument. From then curiosity would eventualy lead to this new Field of Science (Astronomy). Even then much would be theorical and even debated until finaly being able to breach the ice cover.
Considering that even in present Humans can reach the moon and other planets with probes, but still haven't made holes as deep as might be requiered by a civilization in Europa to reach outside the ice cover (and they would be drilling against gravity!) - maybe there could be a significantly developed civilization that knows little of the universe out of the ocean.
Hey maybe there is a mega civilization now on Europa that is as advanced as us or more but has not developed technology or science to breach the ice cover yet. 258