Not so much folklore as Seafaring Lore, tales of mermaids (known as ceasg, literally maid of the waves, according to Scottish mythology) have been around for centuries. Though forming a big part of legend around, amongst other places, the coastal areas of England, the first recorded stories are much earlier, appearing in Assyria (present day Northern Iraq)in around about 1000BC with, perhaps the most famous mermaid of all, Hans Christian Andersen's Little Mermaid, not appearing until 1837.
Depending on the time period and source, merfolk's behaviour can vary drastically but most people agree that they are able to attract humans with their singing - the reasons as to why they do this is what varies considerably.
Just like THE LITTLE MERMAID of Disney fame (pictured above left) mermaids are generally depicted as having the upper half of a beautiful woman with long, flowing hair hanging to the waist with the bottom half of a fish though interestingly enough the merfolk of early English folklore were actually tailless. Often seen sitting on rocks, traditionally mermaids were harbingers of bad luck who it is said predicted stormy, rough seas and, with their beautiful singing, lured men to their deaths. Not all bad though, some believe mermaids are a bit more kindly than this and have the power to grant the gift of magical powers ...... usually at a high price.
Then, of course, there are the Chinese myths that have mermaids whose tears could turn into priceless pearls - needless to say, in this instance, it was the fisherman who tried to lure the mermaids, unfortunately though their song simply put the said fishermen into a coma.
And talking of Chinese mermaids, did you know
But what of mermen?
Said to be much less friendly and with little interest in humans, mermen were portrayed in Irish mythology as the polar-opposite to mermaids in that they were believed to be really, really ugly creatures with pointed green teeth, pig like eyes and a red bulbous nose. Much more attractive were their Finnish counterparts (the vetehinen) who, like mermaids, were said to be extremely attractive individuals.
Also seen as having magical powers some cultures believed mermen were able to cure illnesses, lift curses, and brew magic potions whilst the encantado (literally 'the enchanted one' in Portuguese), were believed to be able enchant human woman and, obviously more interested in humans than the average merman, impregnate them.......
And other merpeople, what of them?
Hmm, lets see.
- The Merrows. Typically the Scottish and Irish equivalent of the mermaid and mermen of many other cultures, the merrows (from the Gaelic murúch), like many other merfolk, are capable of attachment to humans, sometimes marrying them and living amongst them for many years before most generally return to their homes beneath the sea.
- The Sirens. Portrayed as fully aquatic mermaid type creatures in later folklore tales, in earlier Greek mythology the sirens were portrayed as bird-women hybrids who, like mermaids, lured sailors to their deaths with their enchanting songs.
- The Selkies. Though also believed by many to be a merperson the Selkie/silkie/selchie of Irish, Scottish and Icelandic folklore differs from your typical mermaid/man in that they are able to become human by taking off their seal skins, returning back to seal form when it is put back on.
- The merpeople of Hogwarts. In actuality selkies, the merpeople of Hogwarts have grey skin, green hair, yellow eyes and broken teeth. Oh and they are very tall - if I remember correctly the one Harry Potter met was well over 7 feet tall.