I read the short story in an anthology in the 80s or early 90s. In it two lobsters are (I think?) among a mass of lobsters making a religious pilgrimage across the ocean floor and sharing their excitement and perspectives. If I recall correctly, the story is implied to take place on a very post-human Earth. When they arrive at their destination the text describes in an awed tone their living god which is some kind of giant cephalopod atop a submarine hill.
This sounds like Homefaring, a novella by Robert Silverberg published in 1984.
The consciousness of a man named Jim McCulloch is sent forwards in time by millions of years by mistake (the experiment was aiming at an interval of a few hundred years). He awakens in the body of a creature very much like a lobster:
and yet there were differences. They were larger. How much larger, he could not tell, for he had no real way of judging distance and size in this undersea world; but he supposed they must be at least three feet long, and he doubted that lobsters of his time, even the biggest, were anything like that in length. Their bodies were wider than those of lobsters, and their heads were larger. The two largest claws looked like those of the lobsters he remembered, but the ones just behind them seemed more elaborate, as if adapted for more delicate procedures than mere rending of food and stuffing it into the mouth. There was an odd little hump, almost a dome, midway down the lobster’s back—the center of the expanded nervous system, perhaps.
They are intelligent, and appear to be among the highest forms of life in the future world. No creatures with internal skeletons are known - no sharks, or whales, and no humans of course. The lobsters take McCulloch's appearance as an omen, and set off on a pilgrimage.
We have decided that the time of the Molting of the World is soon to come; and therefore we must make the pilgrimage. It is the end of all things. It is the coming of a newer world. You are the herald; so we have agreed.
On the way they do meet their living god, a giant octopus "that must have been fifteen or twenty feet in diameter, with tentacles that extended an implausible distance on all sides." The god tells them that McCulloch's presence is not an omen, merely a mistake, but the lobsters continue with the pilgrimage anyway. When they arrive at the destination, the only area of remaining land on the planet, the lobsters molt in preparation for reproduction, and McCulloch's consciousness is whipped back to our present.