The planet's name was Uyyar, which wasn't massively important. It was a simple, basic planet. There are oceans and land masses, earthquakes and hurricanes. Gravity was medium-shading-to-low, the atmosphere was oxygen-rich and there were gigayears of biodiversity. The most interesting feature of the planet's life was that many of the organisms on the planet were doughnuts. Not literally made of dough, but loops of living matter with large, very obvious holes in the middle. Any carbon-based organism with a one-way digestive system technically has a genus of at least one, and anything with more than one nostril can add one to that figure, but it's seldom possible to see clear daylight, or bare ground, through the thing. Not so, on Uyyar. It was the rule, not the exception. Early on, something had found incredible success with this punctured design, and made it work.
The smallest of the rings were the size of a person's hand. Circled with flagella, they moved through the oceans by rolling, like rubber bands being rolled down the exterior of a pipe, flailing at the water in a manner reminiscent of Earth crinoids. Larger ones moved across swamps and sludgy beaches. They were big circular, amphibious slugs, eating through their fat, circular "foot", moving irregularly. Different parts of the creature sometimes wanted to move in different directions — there was a singular brain at one point along the loop, but clumps of nervous tissue at various points around the edge, making navigation behaviour something of a group decision, like an octopus's tentacles.
Others, proper land creatures, were living rings of muscle, with teeth around parts of the edge. They moved by flipping up onto one side and rolling. A group of them, piled up and sleeping together, looked like a bizarre, furry game of quoits.
But the most startling denizen of Uyyar was orders of magnitude larger than any of them. When first observed, from space, it was (in very preliminary opinions) guessed to be the rim of an impact crater, or some other kind of natural geographical formation, or possibly a wall built by possible now-extinct intelligent beings. It was a tightly winding ribbon of iridescent matter, a rough loop more than five thousand kilometres long and averaging around seven hundred kilometres across, as tall and sheer as a mountain, sixty to three hundred metres thick at different points... and it was, slowly, crawling out of the ocean.
Explorers landed beside its advancing front. They saw a living wall of green and purple and grey hexagonal plates, like snake scales blown up to the size of advertising hoardings, as hard as rocks. There was a sheer wall stretching to the left and the right for kilometres, curving in and out as it consumed the murky, inconsistent, hilly terrain beneath it in similarly inconsistent spurts. It was moving to cover the continent, marsh, beach, forest and all. One tongue of the organism's forefront, for example, was extruding its way relatively rapidly down a river valley, at a snail's pace, while other parts were being slowly dragged up and over hills.
Behind it, in the ocean, it had dragged a trail across the sea floor and the shelf. As monumental as the organism was, it was around the same density as the water, and depending on the movement and expansion of organs inside it, could apparently become buoyant or sink as required. Long loops of it were still hanging off the continental shelf, slowly contracting and rising.
The trail was thousands of kilometres long. It could be followed in long, erratic loops for what had to be centuries. Behind it, the seafloor was visibly altered. It was as if it had been ploughed and seeded. There was more biodiversity, fresh coral growth, fish and crustaceans which appeared nowhere else in the planet's oceans. Flashing orange bugs and brightly striped purple whales. It looked for all the world as if this organism was a critically necessary feature of the ocean ecosystem. Its movement pattern was not deemed to be intelligent, but it appeared curiously systematic. As techniques for following its trail improved, it appeared that this monumental entity had, over the course of tens of thousands of years, "walked" across nearly every square kilometre of the undersea land.
It, or entities like it, had. There were no other such entities in evidence.
It was called Hepht.
Tild, the researcher, lived in a small, mobile hut in the middle of Hepht's inner walls. Hepht moved, albeit slowly, which meant that every few years Tild would need to move her hut. But the area of land encompassed by Hepht, the area of land across which Hepht had dragged its ludicrous bulk, was large, and was so continually full of surprises that she needed to move around to explore every part of it.
Tild's hut was able to both fly and stand upright, indefinitely, above the ground, on a thing called an antigravity pogo stick. Tild walked on the ground for her research, but her hut and living area were all suspended above the ground, sometimes ten metres up, but usually less than a metre. In this way she avoided driving all over the Hepht interior or doing permanent damage. Her system was self-contained. Sometimes she would have the whole thing lift up and move to another area.
Behind the receding front of Hepht's inner wall, there was typically badly scraped land. But a surprising amount of vegetation was able to survive the several months spent being crushed underneath its bulk. Tild's research had discovered why. She had put a chemical probe underneath the front of the wall, waited a year, and then collected it from the other side, and discovered that Hepht emitted chemical nourishment from its underside. The plants were able to survive on that. In fact, underneath Hepht, an entirely different form of non-photosynthetic life seemed to hold sway.
And while growing inside Hepht's boundary, plants grew in a completely different phase. It was if they had been primed. There were more flowers, and brighter leaves. There were species of birds which lived in trees which would only grow inside Hepht's boundary — Tild eventually realised that these birds were just birds from the outside world, but they grew brighter feathers here.
Eventually, Tild realised that Hepht's natural boundary formed a kind of inverse island. There were no predators inside it. Nothing large or dangerous could cross the mountain-like wall or burrow all the way under it. Everything could get on with being itself here.
From space, as decades passed, Hepht became increasingly obvious. On a tropical, rainforested continent which was normally brown and deep green and deep blue — due to an evolutionary divergence, hundreds of millions of years ago, half of the plant life on this planet was blue — Hepht was a bright ring containing nothing but brilliant rainbow colour.
It was an enthralling place to explore. Uyyar was otherwise a disinteresting and uninhabited planet. Tild was one of only a handful of people permanently resident on it, because there were so many easier places to live. Tild was the only person who studied Hepht, enduring relatively intense heat and humidity while everybody else stayed at the relatively cool poles. Hepht's walls had strange effects on air movement, resulting in it even having its own climates, which Tild also studied. The structure of plates at the top of its wall made a rising and falling hooting noise.
But there were serious mysteries. There was no evidence, anywhere on the planet, that Hepht had been out of the ocean before. On no continent was there a trail. Even if it had happened thousands of years ago, it should have been obvious. So, why now? Why had Hepht left the ocean? How long had it really been since it last left the ocean? It must have done so previously, otherwise, how was the plant and animal life adapted to this scenario? Where were all the other Hephts? How did it reproduce?
Tild lived with Hepht for years. She walked along its entire perimeter wall, twice. She realised, after taking careful notes, that Hepht was slowing down. Finally, it stopped. Every part of it stopped moving. It had come onto the land to die.
Hepht, Tild finally concluded after great study, was not unintelligent. The birds and plants of Uyyar were not naturally like that... Hepht had deliberately cultivated them. Hepht had decided to come onto the land and do some gardening. It had altered those trees and plants of its own accord, because it liked them, and it walled out predators on purpose, because it liked to have a place where the brightest birds could live and squawk. It wanted to explore. It wanted to retire.
Tild lived in Hepht's garden for two more years. Then, she discovered at the centre of the garden, a geographical formation she had not seen before. Roughly circular rocky plated worm rings, three of them, slowly disentangling from one another.