Merfolk

Merfolk(人魚 Ningyo) are shown in the world of One Piece as one of the two major races that inhabit the Sea, the other being the Fishmen. Often the term "Fishmen" is mistranslated from Japanese to "Mermen," however the two species are very different. Unlike the Fishmen, the Merfolk are peaceful, and prefer their race to remain a secret.

Like the mermaids and mermen of folklore, their upper half is that of a human while the lower half is that of a fish. As demonstrated recently by Kokoro, mermaids may walk on land as when they are thirty years old, their tails split into two. Like the Fishmen, they are based on the different fish of the Sea; for example, Kokoro is an Icefish Mermaid. Mermaids and Mermen are friends to the fishes of the sea, fun loving and usually get along with most people, including Fishmen (even though Fishmen can often take advantage of the Merfolk's good nature).

So far, the only other members of this species featured is Camie, who was a mermaid the Fishman Hatchan saved twice in the mini-series Hatchan's Sea-Floor Stroll, and Kokoro.