Pelagios

A subspecies of human (Known as a Drift), the Pelagios were once the inhabitants of the deepwater mining stations and farms on the planet Poseidon. Somewhere along the line after the fall of humanity, the survivors must have used extensive gene editing to give themselves a chance at survival, cut off from the rest of humanity as they were. The natural pressures of them planet took care of the rest. 
Now, the Pelagios are noticeably blue in skin tone, with dark hair (on the head at least, the rest of their body lacks hair at all) and eyes. 
They are able to breathe underwater through a set of gills on either side of the neck, as well as draw in water into their lungs and stomach so as to prevent the depths of the sea from crushing them. This water-born pressure is thought to have toughened their bodies as well, with older Pelagios said to be able to deflect knives with their skin.