Great Moving Islands

Mellitus placed the contract on the table, in front of the four wizards. Alistair tapped the contract with a grimace. "How are we expected to project an image this large, of something we've never seen ourselves in real life, and somehow have all five of us mentally synchronized as to what we're projecting?"
"It's our jobs, Alistair." Vera sighed. "It would take some practice, but I think it would be doable to do it in miniature. We'd all just have to study more drawings of these Moving Islands so we're on the same page."
"The same page doesn't mean something larger than the Grand Canal. It would take a hundred wizards to pull this off to any acceptable degree." Alistair raised his fingers. "The largest thing I've ever projected is a power-wagon. This is, what, two hundred times the length?"
Mellitus rolled his fingertips together. "Rigana is capable of projecting a line of power-wagons in a row. Perhaps we'd need about thirty wizards to make the projection?"
Alistair shook his head. "The mathematicians would weep if they heard that line, Mellitus. Projections are in three dimensions, not one. We would need nine hundred wizards of Rigana's strength to cover length and width to any satisfaction. We have, perhaps, six? As strong as her."
"So what do you propose, then, Master Archmagus?" Vera had a hand on her face, in some irritation. "We can't up and reject this request, it came from the Hall of the Princeps itself. Conjure an image of a Great Moving Island, in order to show people what they must have been like. Are you going to tell the Princeps no?"
"If I have to. I've done it in the past." Alistair blinked. "I propose we do something else to impress the scale on the viewer. Something that will fill a warehouse or a grand ballroom, and we project images of people on their backs in order to get scale. With some artists from the Academy and some practice, we could pull this off, just the five of us in this room."
Mellitus nodded. "A promising approach. Take the lead and find an artist. I'll head back to the Hall, see if I can't convince Constantine of his folly."

Basic Information

Anatomy

Great Moving Islands were easily the largest known animal, colossal leviathans of the sea, only known to be actual animals and not some kind of strange natural phenomena due to occasional instances of beaching. These animals are colossal whales, unusually wide and flat, with four sets of fins and a massive, always-open mouth that draws in smaller animals directly into their first stomach for direct digestion. Unlike any other known whales, these leviathans were likely incapable of diving underwater; no recorded instances of this happening exist in the naturalist's record.
It is difficult for words to describe precisely how enormous these animals were. Larger than any other animal, larger than any ship that has ever been built, larger than many small villages, it could take an hour for a person to walk from one end of the Island to the other. They are large, semi-ellipsoid, and much flatter than any other whale, providing the characteristic shape from a distance that makes them resemble a sandbar from a distance.

Growth Rate & Stages

No other animal has ever existed that was even close to the same size as these Moving Islands, and reasoned conjecture about megafauna postulates that it must take decades before an animal could grow to the appropriate size.

Ecology and Habitats

The Great Moving Islands were witnessed in all corners of the Feryll Sea, preferring the deeps of the ocean over the comparatively shallow Bui Sea encircled by Eastern Saibh. They were exclusively surface animals, skimming the waters for food, their backs perpetually dry and above water, and their underbellies always below. They seemed to express no preference as to temperature, being spotted near the southern ice caps and near the boiling waters of volcanic mounts in equal measure.

Dietary Needs and Habits

Great Moving Islands were surface feeders, eating essentially whatever entered their mouths, which scooped up anything in front of them just above or below the surface of the water. Historical observations have repeated similar tales of these leviathans eating anything - fish, seabirds, random flotsam, all of it simply enters the Moving Island's mouth, never to emerge again. Basic mathematics regarding their size implies that they must have spent essentially every hour of every day constantly eating in order to grow and maintain their colossal bulk; Moving Islands likely represent the upper bound of what is physically possible for an animal to be sized.

Behaviour

Despite their enormous size, Great Moving Islands exhibited almost no meaningful behavior to speak of, leading many in antiquity to believe that they were not animals at all, but some sort of large aquatic plant. This was definitively disproven by an account recorded sometime in the 200s, when a pirate of The Stagonids recorded an incident where she mistakenly rammed one of these animals while commerce raiding. By this account, the animal turned and attempted to swallow the pirate's carrack whole; the pirate only managed to escape once she realized what the animal was attempting to do; she noted that the induced current was 'fierce and unrelenting'.
Other than such actions at large scale, Moving Islands were unusually pacific, with many recorded accounts of people setting up camp on their backs, lighting fires, and otherwise engaging in activities that would be bothersome to any animal were they not at this magnitude of size. The animals simply drift in a vague direction, consuming everything they come across, and ignoring the activities of all other animals the way a person may ignore the activity of insects. Even enormous predators such as the Great Nautilus seem to have not been capable of inflicting any serious harm on a Moving Island.

Additional Information

Social Structure

Reasoned conjecture states that these animals must have successfully bred, but no Moving Island has ever been seen in the company of any other, in any historical account. These were solitary animals, drifting alone in the currents, and must have somehow acted in a way to maintain this solitude, as by sheer chance and number of sightings, an account of two within eyeshot of each other should have occurred at some point in history.

Uses, Products & Exploitation

Great Moving Islands were the stuff of tall tales and legends throughout recorded history, with stranded sailors washing up on their backs and using them to ride back to shore, intrepid explorers camping on them, content to see where the Island would take them, and naval ships using them as cover in early naval battles. The animals were simply too big for anything that could be considered exploitation, instead simply being treated as an ineffable natural phenomena, a piece of land that may not be there the next day, a shipping hazard that moves with the current. Exactly one Moving Island was ever discovered as beachkill, and its skeleton was so enormous as to defy description; the bones were themselves too large to cut or manipulate, and the whole carcass was eventually washed back into the ocean.
Moving Islands were principally used as curiosities, as they were a relatively common sighting across most of history, up to the petty kingdom era. Fishers would tie their boats alongside and fish from their backs, and adventurers would set up camp on their backs on occasion - one specific Moving Island was known to follow what is now known as the Great Circular Trade Route, and taking a small canoe to the Moving Island and riding it around the continent was faster than booking passage on a cog. This particular Moving Island did eventually stop following the route, to the great consternation of the people that were on its back at the time.
Moving Island sightings began to slow around the time of the petty kingdoms, and the last known sighting of a Great Moving Island was during The War of Unification, a solitary Moving Island spotted by a group of Etoilean Navy Siege-sails deep in the northwestern Feryll Sea in the year 629. It is unknown if they are actually extinct, have simply migrated to a different part of the world, or are reacting to something in the Principality of Etoile. The latter is considered ridiculous, of course - why would an ocean animal care a whit about a political shift between humans on land?
The Academy of Etoile requests that any sightings of a Moving Island be reported to it immediately, in order to launch a expedition for study and confirmation that the species continues to exist. Three expeditions have been launched in response to sightings, but have turned up nothing.

Geographic Origin and Distribution

Great Moving Islands were found in all deep seas surrounding Saibh, with multiple verified accounts of their passage past ships and port towns.

Average Intelligence

If they were intelligent to any measure, there's no telling. The pirate ramming account remains the only recorded instance of this animal responding to stimuli at all. Unlike other, smaller whales, there's no account of the Moving Island ever vocalizing.

EXTINCT

Lifespan

At least 700 years

Conservation Status

Extinct for all practical purpose

Average Height

~70ft from breathing hole to underbelly

Average Weight

Unknown, estimated in the >150 megaton range

Average Length

2500-4500ft