Mermaids are a species of aquatic humanoid creatures that exist on Ephedia, as mentioned in Sirens.
Appearance[]
No mermaids were seen in the show, but it's known that they are creatures with the head and top half of a humanoid, and instead of legs they have a large fishtail. Their tails can be many different colors and possibly their hair could be too since they live on Ephedia. They are also very protective about their aquatic habitats, as Auriana mentions; 'Mermaids are a species of girls with fishtails who clean the ocean...'