Merfolk originate in the Endless Ocean layer of Lamannia, but have been pulled into Eberron repeatedly throughout the world's history, becoming stranded in various oceans and unable to return home. They can be found across Eberron's oceans, and even in Khyber's Sea of Sorrow. There are several distinct Merfolk cultures found across Eberron's oceans, with the Kalamer in the Thunder Sea being the most numerous of the surface oceans.
Merfolk are aquatic humanoids, with fish-like skin and tails (instead of legs), and with gills on their necks. Their lungs function as swim bladders, as well as allowing them to draw oxygen from air when they find themselves out of the water. All merfolk are connected to Lamannia, regardless of their current location, and this makes them naturally gifted druids and rangers, and some rare merfolk are called by the elements to restore balance out of the water, and gain the ability to transform into a fully humanoid form.
The merfolk of Cartilay are a distinct culture of their own, and over time they have adapted to the subterranean, deep sea environment they call home. Bioluminescence is common, as well as large, bulbous eyes that capture as much light as they can.