Yes, there are mermaids…and then there are a host of “mermaid types” – maidens of the deep who clearly derive from the same pool of myths and stories as mermaids. However, they have distinctions that are fascinating, and, I think, important. I hope you enjoy the summary of each below!
Selkies, from the Orkney and Shetland Islands, have seal skins that they can take on and off at will to become human. If their seal skin is taken, they cannot return to their homes in the sea, but must stay with the mortal who has their skin. In this respect, they are very much like swan maidens, who have the same rules associated with their swan feathers. This indirectly links selkies with the sirens, whose distinguishing features are their feathers (although sirens do not transform).
In the old tales, they are far kinder and more noble than mermaids. They do not try to take people captive, or bring destruction on those who harm them.  In fact, the selkie women are the ones who have to fear; there are many tales of mortal men stealing a seal skin of a selkie maiden.
It’s easy to see how selkie stories got started. Seals’ upper bodies have “a startling likeness” to a human form, especially when “in the foggy atmosphere of the northern seas.” They have a “merry, playful disposition,” but are rather “timid.” They can be taught to speak, and they love music. All of these are qualities of selkies.
Fun fact: seals also steal humans, as this event shows:
While in Constantinople, “a drunken sailor was sitting astride on the cask [of wine], and singing boisterously, when all of a sudden the seal raised himself out of the water, seized the sailor with his left arm, and threw himself with his prey back into the waves. He reappeared at some distance, still holding the man under his fin, as if wishing to display his agility, and then sank once more, leaving the frightened, sobered sailor, to make his way back to the boat….if the same, even had happened in earlier days, the seal would have been a beautiful Nereid, who, having conceived a passion for the hapless sailor, had risen to take him down to her palace under the waves.”
And just like that, the story would have taken off…but would probably end tragically, as so many of the mermaid relationships do.
Merrows, or Moruachs, are the Irish derivative of mermaids. Although the name comes from muir meaning sea and oigh meaning maid, they are slightly different from our typical mermaids. First off, merrows have a “pleasant disposition” and they “lack the tempestuous and sometimes malicious nature expressed by mermaids from other locales.”
The shape of the merrow is a bit unclear. One story describes them as green and having “a fish’s tail” as well as “legs with scales on them.” Another shows that although the girl can walk, she is clearly a fish. Although the fact that she has green hair may have been the giveaway in that case. However, some stories don’t mention any such descriptions, and merely call her a beautiful woman.
Like the selkie, the merrows have an item that, if taken, makes it so they must stay with the person who takes it. It is called a “cohuleen druith, or a little charmed cap, generally covered with feathers, and used for diving underwater.”
This is actually quite significant in relation to the sirens. In one of the Greek myths, the sirens lost a singing contest to the Muses, who in turn “pitilessly tore off their wings” and made crowns out of the feathers.
Did this myth come after the Greeks had interaction with the Celts? Or is the merrow the Irish counterpart to the Greek Muse? Not sure, but possibilities abound.
Both nix and undines come from Germany, and are similar enough to put in the same category. A nix (or nixie, neck, neckan), is a “water-spirit of Teutonic mythology” who lives in “lakes or rivers.” It seems they are generally male, since Heidi Anne Heiner’s Mermaid and Other Water Spirit Tales from Around the World, only lists one story of a female “nixie,” which was written by the Grimm’s Brothers. An undine, on the other hand, is a female spirit who “resides in the water.”
Both are able take a human form, and the stories of them often show them seeking a soul (i.e. salvation). The undine can only attain salvation through marriage to a mortal. Although the nix does seek salvation, he does not do so through marriage; however, there are stories of nix taking Christian women as wives.
Occasionally you see undine’s described as French water spirits, but that is not so. The first recorded use of the word undine was Paracelsus, a Swiss physician and alchemist. He relates a German poem written by Egenolf von Stauffenberg to prove that an undine’s “relationships with men are ruinous,” as apparently one of Egenolf’s ancestors died from an undine’s curse. The reason why it’s sometimes considered French is becauseof Baron Friedrich de la Motte-Fouque’s tale. He was of French descent, but grew up and lived in Germany. His story has explicit Germanic references, and so undines should be seen as Germanic water spirits.
Rusalkas, as the name implies, are of Russian origin. They have green hair and live in lakes and streams. They are associated with weaving, spinning, and washing, and the week before Whitsuntide (Pentecost) they ask for linen garments (see banshee below). Like many mermaids, Rusalkas have combs, with which she can “produce a flood” and thus always keep her hair wet (because if it dries, she dies). The Rusalkas, however, are associated with the harvest, which the other counterparts never are.
They lack a tail, and seem to be more apparitions than any of the other aquatic spirits, and some legends even say they are “female ghosts who haunt lakes and rivers” after a woman dies an unnatural death. (This will become important for the banshee category.)
The Russians have another water spirit called Tsar Morskoi, who lives in seas, lakes, and pools. His daughters, who are “of exceeding beauty,” are Swan maidens with “feather dresses.”  Thus, these water spirits are clearly linked to the sirens (and possibly to the Irish merrow, although distantly).
Yes, that’s right, banshees have a water quality. The Fualh-a-Banshee is a “water-maiden with web-feet, and long yellow hair,” and is “evil-minded.” They share a clear connection with the Rusalkas, listed above. But are they mermaids?
The one extant story we have of a banshee-mermaid is Melusina, who was a mermaid (but only on Saturdays). However, she is also said to sprout wings during that time, making her both mermaid and siren. When her husband discovered her secret, she became a banshee, and can be seen flying over Lusignan castle whenever one of its lords is about to die. Several articles assembled in Heidi Anne Heiner’s Mermaid and Other Water Spirit Tales from Around the World mention this connection.
Banshees also bear resemblance to a certain “mermaid of Loch Slin” in Scotland. In this story, a girl saw a woman “beating clothes on a stone” (probably to dry them). This is a connection to the Rusalkas, who are associated with linens and washing. The banshee portion comes in with impending death: the “mermaid” has 30 linens with blood on them, and on the next Sunday after seeing the “mermaid,” an explosion killed 30 people.
So yes…it seems that banshees can be classified as a mermaid-type.
Non-European Mermaids and Mermaid Types
Are there mermaids in non-European countries? You bet! They don’t get as much publicity as European ones, but they are fascinatingly similar. Many of them have combs, mirrors, and temper tantrums just like European mermaids and mermaid types.
Although they are less studied then the European counterparts, they undoubtedly stem from the same gene pool as our own mermaids. I’ll post more about these in my current blog, but just know this: they are also part of God’s plan for the mermaid.
 Scottish Mermaids by R.J. Arnott, Heidi Anne Heiner’s Mermaid and Other Water Spirit Tales from Around the World (Nashville, TN: SurLaLune Press, 2011), 199.
 The Mermaid Wife, Ibid., 175.
 Mermaids and Mermen from Credulities Past and Present by William Jones, Ibid., 65.
 Scottish Mermaids by R.J. Arnott, Heiner’s Mermaid, 201-202.
 Fables and Facts from Wonders of the Deep by Maximilian Schele de Vere, Ibid., 39.
 Fables and Facts by Maximilian Schele de Vere, Ibid., 40.
 Ibid., 41.
 Skye Alexander, Mermaids: The Myths, Legends, and Lore, (New York: Adams Media, 2012), 14.
 Ibid. 97.
 The Soul Cages, Heiner’s Mermaid, 263.
 The Lady of Gollerus, Ibid., 252.
 Donald and the Mermaid, Ibid., 285-286.
 The Merrow-Maiden and Merrow-Man, Ibid., 232.
 Meri Lao, Sirens: Symbols of Seduction (Rochester, VT: Park Street Press, 1998) 30.
 The Neckan by Mathew Arnold, Heiner’s Mermaid, 365.
 The Peasant and the Waterman Ibid., 523.
 The Nixie of the Mill-Pond, Ibid., 529.
 Lao, Sirens, 130.
 The Neckan by Matthew Arnold and The Mermaid and the Boy, Heiner’s Mermaid, 364, 366, 488.
 Lao, Sirens, 129.
 The Neckan by Matthew Arnold, Heiner’s Mermaid, 364.
 Lao, Sirens, 130.
 Russian Water Spirits by W.R.S. Ralston, Heiner’s Mermaid, 509.
 Russian Water Spirits by W.R.S. Ralston, Ibid., 509.
 Ibid., 510.
 Alexander, Mermaids, 129.
 Russian Water Spirits by W.R.S. Ralston, Heiner’s Mermaid, 512-513.
 Water Sprites and Mermaids by Fletcher S. Bassett, Ibid., 120
 Melusina from Curious Myths of the Middle Ages by Sabine Baring-Gould, Ibid., 13.
 Lao, Sirens, 126.
 Melusina by Sabine Baring-Gould, Heiner’s Mermaid, 11.
 Melusina by Sabine Baring-Gould and Water Sprites and Mermaids by Fletcher S. Bassett, Ibid., 7, 120, and 139.
 Scottish Mermaids by R.J. Arnott, Ibid., 197.
 Ibid., 197-198.