i think one of my favorite sapient species in my setting is. this one pre-FTL species that's based kinda loosely on various cephalopods
first off, the planet they call home is a bit of an ocean world - over 90% of the surface is covered in liquid water, and there's no polar ice caps. the scattered islands across its surface are mostly volcanic, as it is a very tectonically active planet. there's also a few groups of atolls and reefs scattered around, created by a genera of life on this particular planet that's evolved a life style similar to that of earth corals, though there's one standout that forms colonies so large that they eventually collapse under their own weight and form more surface areas for others to colonize (as well as innumerable tunnels beneath where some species have adapted to live).
these cephalopod-like sophonts are, at the setting's "present day" (~2500 in Earth years on our irl calendar), in the midst of their iron age. they refine and work metal largely through heating it on volcanic vents, and their cultures are numerous and varied.
they largely communicate through color patterns displayed on their bodies and perceived through their pentachromatic eyes, though they're also known to use microtonal noises produced by a specialized organ their family's last common ancestor developed. they can also take very short trips onto islands thanks to a sort of proto-lung they have, but must return to the water quickly lest they dry out.