Mermaids

 A mermaid is a legendary aquatic creature with the upper body of a woman and the tail of a fish.^[1] Mermaids appear in the folklore of many cultures worldwide, including the Near East, Europe, China, and India. The first stories appeared in ancient Assyria, in which the goddess Atargatis transforms herself into a mermaid out of shame for accidentally killing her human lover. Mermaids are sometimes depicted as perilous creatures associated with floods, storms, shipwrecks, and drowning. In other folk traditions (or sometimes within the same tradition) they can be benevolent, bestowing boons or falling in love with humans.

while looking through wikipedia i also found this interessting view on mermaids
The One Thousand and One Nights collection includes several tales featuring "sea people", such as "Djullanar the Sea-girl". Unlike depictions of mermaids in other mythologies, these are anatomically identical to land-bound humans, differing only in their ability to breathe and live underwater. They can (and do) interbreed with land humans, and the children of such unions have the ability to live underwater. 
I do believe that sightings of mermaids during the history of men is caused by lack of vitamins, dehydration and just missing female companions while being on a ship for months. Even a seal can look like a woman then.
but that doesn't make mermaids less interesting or beautiful.

* also interesting I've learned that children who have gender issues are called mermaids as well.
quit a cute name i must say.
* pictures from google