Merfolk

Merfolk, with the males being mermen and the females being mermaids, are humanoid creatures who live in the ocean. They are usually depicted with the head and torso of a human and the trunk and tail of a fish, manatee, or seal. There is no single original source for merfolk legends, which have arisen independently among nearly every seafaring culture in the world. The oldest known written sources for mermaid-like creatures come from China in the 4th century BC, although there are ambiguous references to vaguely icthyoid sentient beings in Homer's Iliad and Odyssey, and the Philistine god Dagon, both from the late 2nd or early 1st millennia BC. Cultural ideas about the precise biology and nature of merfolk include an infinite number of variations.

Merfolk in "Leg Irons, the Bitch and the Wardrobe"
The kingdom next door to Leffing had a merfolk population of its coast, including a well-known opera singer.

Merfolk in State of Jefferson
Merfolk were a sentient species of the order Sirenia, related to dugongs and manatees. A noted merfolk population lived in the north Pacific Ocean off the coast of Jefferson, USA. Merfolk vocal chords were unable to reproduce sounds of human (or Sasquatch) speech, but merfolk were capable of literacy in languages such as English.