A few of the sapeint underwater denizens of Gaia. (Sidenote: I’ve decided the planet of mlp needs a better name, as I’ve just called it Equus until now. So I guess I’m ripping off Earthsong now. It’s just such a good and fitting name for my nextgen verse -it’s an alternate reality version of our universe, and the way it differs is partially the result of Discord’s messing with it. Gaia is the greek version of Tellus, and in some iterations she’s the daughter of Chaos. See, it, it rhymes. )
 
Anyway, back to the main program. This isn’t near all of them, just the most prominent to land-dwellers/common/interesting. With the surface of Gaia being like 70% covered in water (like our Tellus), there’s a lot of creatures living underwater, which just by sheer number means there’s a lot of sapeint creatures down there as well. However, many live so far down that those living closer (or above) the surface cannot dive down far enough to reach them; vice versa, with them being unable to travel up. This could probably be solved with magic… except, they’d have to know about each other for them to want to. Which most don’t. So they don’t know about each other because they can’t meet, and they can’t meet because they don’t know about each other. Each “layer” only really know about the “layers” adjacent to themselves, and maybe one further away by talking to the neighbour layers. It’s a big ocean.
 
Still, there’s plenty close-to-surface dwellers! There exists many underwater countries alongside the coast of Equestria, some consisting of just one or two species, some being a rainbow of different creatures. Many cities surround and go over islands, and thus consist of both land~~, sea~~ and amphibious inhabitants. Not to mention the cities and villages in Equestria’s larger lakes.
 
Mermares and Kelpies  
To start with, there’s many equine composite underwater creatures (collectively known as Hippocampi). The most notable ones are the Mermares and the Kelpies. Mermares are very common, and can be found in underwater countries bordering on Equestria. They’re very social omnivores that have mostly a good relationship with land-dwellers, with much trade occuring between the people. Kelpies are a lot rarer -while they appear similar to Mermares, they are very different biologically. With them being a combination of Horse and Lionfish, they are venomous and mainly solitary, living on various coral reefs. They also have the ability to hypnotise prey, wish they use to lure fish close enough to sting. They’re carnivores, and most don’t like other sapients (though it varies by individuals). There’s many stories and legends of them also luring land-dwellers into the water to drown and eat, though there’s never been an actual documented case.
 
Seaponies  
Then in the equine-club there’s also Seaponies -our favourite shapeshifted Hippogriffs. And sometimes ponies -or, really only one pony. Sweetie Belle refuses to say how much she had to pay to buy a piece of the Pearl for Scootaloo. Scootaloo also doesn’t ask, but is often seen just staring at the piece with a soft and wonderous look on her face. They don’t live in Seaquestria, but has a house right next to Ponyville lake and often take trips to the ocean. (Sidenote2: I decided to change the ponies’ appearence when in Seapony form -I just really like the curly seahorse tail darnit, it’s cute, and noone can stop me)
 
The pearl was originally created by three very powerful Hippogriffs thousands of years ago -they were experts in crafting powerful spells into jewels, including rubies which would let them hypnotise people like the Kelpies and absorb the energy of their victims. When they were caught, they grew and enchanted the Pearl and fled underwater, hoping to excape consequences. They failed, as Starswirl managed to hunt them down and cast through a rift in reality. Everyone had thought they’d died, until Twilight found they’d just been terrorising another universe all this time. The Pearl was kept by the Hippogriffs, being passed down from leader to leader, until present day. Twilight’s plan to use it to change ponies into creatures that could fight wouldn’t have really worked, as all the Pearl is designed to do is change the body-plan of a Hippgriff to a Seapony and back. Ponies and other equines also work, as they’re close enough, but for other creatures it just kinda freaks out and makes straight up fish -like Spike! It broke from overuse, but the pieces still hold the spell-matrix and can be used to transform a couple of people at a time, provided magic.
 
The Seaponies’ existance is …controversial to put it lightly. Many of the “true” sea-creatures are very distrustful of the Hippogriff and their shape-shifting, and most underwater countries are currently pretending Seaquestria doesn’t exist. Still, there are some that has accepted them and even moved to the new country.
 
Octopi and Toothed whales  
Such as the sapeint Octopi and Dolphins. All toothed whales are sapient (here represented by a Dolphin and a Narwhal), and they are very sympathetic to the Seaponies. They are, after all, air-breathers despite living underwater and many other sea-creatures scorn them for it. Many of them moved to Seaquestria after it was first established. The sapient octopi are less sympathetic and more just… seeing another place they can now live. They find most creatures okay as long as they won’t eat them -because they have a pretty big problem with that. There’s both sapient and non-sapient octopi, and many creatures will happily eat the non-sapient ones. And while the sapient variety does look different (with fin-like structures and different-placed tentacles) a hungry non-sapeint predator won’t care.
 
Selkies and Sea Lions  
Another species facing this problem is the Selkies. Selkies are sapients which (when wearing their skin) look exactly like Seals, which are non-sapient. They are also very friendly towards the Seaponies, as they share the ability to transform between and aquatic form and a horse-like land-form. Not many live in Seaquestria though, as they prefer a more nomadic lifestyle.
 
Alongside the selkies, there’s the Sea Lions (once again inspired by Earthsong here). These were created back when baby Discord was playing pin-the-body-part-on-another-body-part (See more about this in my headcanon regarding horses). They are sapient, and live together with the Selkies, much like how the three different Pony-types do. They can’t have kids with one another, but intermarriges are still very common and not out of the norm. How this arrangement came to be is unknown, but the most common theory is that that there used to be Sealion (the normal version) “Selkies” which were disassembled and reassembled by Discord into the new version -the unaffected Selkies would then have chosen to not abandon the new Sea Lions (as many creaturs did with their new composite companions) and continued to live together. The second most popular theory is that Sea Lions are distinctive -if you want seal-hunters to not accidentally kill you, it’s beneficial to have member of the family which is instantly recognisable and shows that you are, in fact, the sapient version. And Selkies have the advantage of being able to go on land, so it was a mutually beneficial relationship.
 
Incidentally, seal-hunting is forbidden in most parts of the world, despite how much food the animals could supply. Most people don’t want to accidentally murder someone. Still, most Selkies are paranoid and will often wear ribbons and such to mark their sapience.
 
Seacows  
Another creature which came into being as a result of Discord is the Seacows. They’re very social, and often lives in towns in Equestria’s lakes and rivers. Like the dolphins, they are mammals and breathe air, and thus a bit of an outcast from the other seacreatures. So they really like Seaponies and many has moved to Seaquestria. Unile their land-counterparts, they cannot produce milk at will -they just hold down normal jobs instead, no extra income for them.
 
Underwater Serpents  
These giant creatures are somewhat related to dragons, which you might not think at first. Dragons are very solitary and generally don’t like other sapients. They value strength and being rough and having a lot of stuff. Underwater Serpents and friendly to other creatures, and enjoy nothing more than a well-groomed moustache and mane. You’ll start to notice the family resemblence though if you ever see two of them meet each other -they enjoy being with other creatures, yes, but cannot tolerate other Serpents. They each have their own territory, and will not allow anyone else trying to take it. They only ever meet to have kids, and mates are picked based on how well-groomed they are. Eggs are laid somewhere, fertilized, and then half is taken by each parent back to their territory. Serpents also eat gems and can shoot/“breathe” boiling water at their enemies.
 
There’s one Sea Serpent currently living in Seaquestria -though she actually lived there before the city was built. But, seeing as they’re not Serpents, she’s happy to have new roomates. Especially ones that can appriceate her gorgeous moustache and give tips on how to make it silky-smooth. Her fondness for the Seaponies is one of the main reasons all of the neighbouring underwater countries have left them alone. Boiling water really hurts, even underwater.