"Loki" is just what I had in mind.

You may recall a sketch I wrote during the Age of Wiki, or maybe even earlier, about a marine civilization called the Coela. The Coela were not a specific organism, but a commensal collective similar to our own corals. Their technology was based on acoustics, genetics and biochemistry, and their machines were specially-bred reef creatures. Their cities and public works were reefs similar to our own barrier reefs, and communication was by means of current -borne pheremones. Industry and agriculture had analogues in plant and animal husbandry of reef organisms.

The entire reef was sentient, but the individual polyps were like our cells, but much more primitive The Coela are highly advanced, with science, mathematics, art and philosophy, they have a history and a politics with other colonies, and a profound understanding of their environment, but the "speed of thought" is so slow human explorers to their planet do not even recognize them as sentient, and they are not even aware of us, except as a new and deadly form of weather. The Coela have a highly advanced geology, some meteorology, but no astronomy. And their tech is not recognizable as such to us. We dynamite and dredge their cities to make harbors and breakwaters.

I'll go look and see if I saved a copy of the post somewhere.