The only thing that prevents merfolk from being a primary species is their inability to travel above the water, a problem rectified by the aqahartis. Similarly to the dwarves, while merfolk exist in all oceans of the world, thousands of years of segregation has led to distinct differences between the different races of merfolk. They range from the relatively friendly and industrious merfolk of the Inland Ocean to the fierce, warlike merfolk of the Western Oceans.
The merfolk were originally born from elven kind. Hinchipol, a deity that enjoyed frolicking with mortals, had granted power to a number of high elf scholars. They devised a plan to enter the oceans, and asked for Hinchipol's blessing. He happily gave it to them, and several thousand elves willingly entered the ocean and became merfolk. Following their entry into the ocean, they quickly realized just how poorly-off they were. Without the ability to create fire, they were helpless against the massive and deadly creatures of the ocean. Desperately, the scholars called out to Hinchipol, but he didn't answer. In the end, it was a god named Tirronfin that came to their aide, granting them the ability to use their voices to create magic unlike anything seen before. They could cast illusions to hide themselves from the monsters of the sea, they could even use their voices to cook food and craft weapons. As they adjusted to life, they spread out, eventually filling the oceans as far as the eye can see.
Characteristics that are the same across all merfolk:
Unusual Characteristics: - While their upper bodies are humanoid, their lower bodies are that of a fish. - Merfolk possess gills on their necks to breathe while underwater, and lungs to breathe while above. However, in order for this to work, they must drain the water out of their mouth and throat once coming above the waves, a process that many land-dwellers find disgusting.
Coloring: - Green and blue scales, with lighter colors of skin.
Lifespan: - 60-70 years
Tails: - Horizontal, allowing for a more steady but slower movement.
Other notes: - The merfolk of the Inland Ocean mingle with land-dwellers more than any other species, due primarily to their close proximity to so many other countries. That said, they are often viewed with disdain by the other species, primarily for this exact reason, but also due to the fact that the aqahartis were a split from that particular culture.
Northern ocean merfolk:
Length: - 5-6 feet
Coloring: - Brown and grey scales, with paler colors of skin.
Lifespan: - 70-80 years
Tails: - Horizontal.
Other notes: - Merfolk of the Northern Ocean tend to be have large quantities of blubber, allowing for survival in the frigid waters. They occasionally trade with the merchants of Sintison and Elsinor, but usually keep to themselves.
Eastern ocean merfolk:
Length: - 7-8 feet
Coloring: - Grey and black scales, with slightly darker colors of skin.
Lifespan: - 60-70 years
Tails: - Vertical, allowing for much swifter movement.
Other notes: - The merfolk of the Eastern Ocean are some of the most elusive of all of them. This is likely due to the prominence of the dark elves and the Scorched Lands along the eastern shores, none of which are particularly friendly. Those merfolk that do approach trading ships will often try to lead them astray or turn them back to the mainland, though it isn't known why. The handful of vessels that have tried to sail straight east have all either been destroyed, or have never been heard from again, leading to much speculation about what the merfolk may be hiding.
Western ocean merfolk:
Length: - 8-10 feet
Coloring: - Red, blue, and yellow scales, with darker colors of skin.
Lifespan: - 50-70 years
Tails: - Vertical.
Other notes: - Due to the fact that the western coasts of Calsin are lined entirely with orcs, vampires, werewolves, aqahartis, and giants, the merfolk of the western ocean are extraordinarily hostile to land-dwellers. Only a small handful of encounters have ever been made that haven't resulted in bloodshed, which has resulted in the western oceans by and large going unexplored. Researchers (usually wizards using calming spells) have managed to get the western merfolk to admit that there's something out in the ocean that they don't want the land-dwellers getting their hands on. Even under duress or heavy illusion spells, though, none have ever revealed the secret of what that might be.
Southern ocean merfolk:
Length: - 3-4 feet
Coloring: - Yellow and orange scales, with lighter colors of skin.
Lifespan: - 30-40 years
Tails: - Vertical.
Other notes: - All that is known of the southern merfolk are records left by ancient researchers. Around the same time as the Dwarven Civil War, the merfolk of the southern ocean simply vanished. No one knows if they went extinct or if they simply fled. Land-dwellers with waterbreathing spells have gone into the tropical waters, reporting expansive ruins of a culture that seemingly perished in its prime. Other merfolk refuse to enter the waters, stating that the ruins have been cursed. Sailing south in exploration has never been successful, as regular and quite powerful tropical storms prevent such exploration by boat, and traveling underwater for extended lengths of time isn't feasible for land-dwellers (the longest anyone has managed to stay underwater is two months, though after a week, the wizard's skin was beginning to peel off from the water saturation. He had to build a suit to keep himself intact, and in the end, he died immediately upon exiting the pool). For now, the secrets of the tiny southern merfolk will remain a secret.