A Darkling Sea by James L. Cambias. It takes place in an unspecified not-too-distant future, after interstellar travel (involving something called "gimelspace") has been developed and contact made with at least one other high-technology species, the Sholen. They and the "Terrans" have established some agreements regarding non-interference with other alien worlds. Humans in a small research station are exploring the under-ice ocean of a Europa-like moon orbiting a gas giant in another star system (not the home system of either the Terrans or the Sholen).
Beneath this dark ocean, many forms of life have evolved, all based on energy and chemicals coming from thermal vents, similar to those found in parts of the Earth's deep-ocean seabed. But in addition to simple worm-like and fish-like creatures, the thermal vents of Ilmatar also support a crab-like intelligent species who navigate and communicate with sound (no light, so vision has not evolved here), and who seem to possess social structures and simple technology, including a form of agriculture. In compliance with the non-contact treaty, the humans have studied the Ilmatarans from afar, but some of the researchers want to get much closer, and this leads to a tragic incident that provokes conflict with the Sholen.
I won't give away more of the story, which is told in alternating points of view of human, Ilmataran, and Sholen characters. The Ilmatarans have a very old culture (millions of years), and although their technology is quite limited (no deep-water electronics!), they have language (including a writing system based on knots tied in fibers), agriculture (cultivating various plant-like species in settlements built around active thermal vents), the ability to build various structures, and a social and legal system. Landowners have apprentices and servants, and markets exist to make use of surpluses and division of labor. There is an education system of sorts (though child welfare is in a sorry state, with many of the very young apt to be eaten by adults or other young), and there is even a tradition of science, mostly focused on the study of life forms and thermal vent systems.
The Ilmataran scientists are very curious, though they cannot imagine that there are other intelligent life forms in the universe, or indeed that there is a "universe" beyond the thick ice layer above them (which they assume extends to infinity). There ultimately is contact and communication among the three species, and quite a bit of conflict and action. Although there are aspects that require substantial suspension of disbelief (e.g., gimelspace is barely mentioned, but it must provide a path through spacetime that allows faster-than-light travel), it's a well-constructed hard-SF world with no annoying "magic" stuff -- a very engaging and satisfying first novel.