Jessie Bayes, The Marriage of La Belle Melusine
Before 2011 I had never heard the names Melusine or Melusina before. Maybe it's because I'm American, and the legend is better known abroad, specifically Northern Europe. She is a fresh water spirit, including rivers and springs, sometimes half-fish and sometimes half-serpent, occasionally with wings, but definitely considered a fairy. She appears on many Coat of Arms, including some in Germany. In Poland this was because she was supposedly the water spirit from the Vistula River in Poland, who identified the place to build for Boreslaus (Boleslaw) in Masovia in the 13th century.
Jean d'Arras wrote an extensive literary musing of Melusine around 1382 based on oral tales - Le Roman de Melusine. In these stories her mother was the fairy Pressyne (Pressine, Pressina), discovered by King Elynas of Albany, and they were married. When the king disobeyed her marriage condition - not to view her giving birth or bathing their three female triplets, she left the kingdom for Avalon. Melusine and her sisters Melior and Palatyne grew up in Avalon, later taking revenge on their father. Their mother punished them, and this is how Melusine took on the shape of a mermaid (half-serpent or half-fish).
Later, similar to her mother's tale, Melusine is discovered by a man named Raymond of Poitou (or Duke of Aquitaine) and he proposes marriage. In the Romans of Partenay from about 1500, Melusine agrees, with the condition that he could not see her on Saturday (and/or while bathing), and she builds them a castle overnight with her magic. Later she builds the cities of Partenay, Mel, Lusignan, and Rochelle. Melusine and Raymond have ugly male children together that go on to do great deeds and marry well. Raymond (of course) breaks his promise and sees her true form (on a Saturday), but she forgives him until he insults her scaled lower-half in court. She takes the shape of a dragon, leaves him with a prediction of the family's decline, and flees.
Melusine was considered the Queen of forest of Columbiers. In Sir Walter Scott's version, Melusine's husband is named Guy de Lusignon, Count of Poitou. In all versions mentioned thus far, Melusine and her mother seem very family oriented, and Sir Walter Scott even mentions that Melusine protects her descendants. In some versions she would act like an Irish banshee, warning her descendants that their death was near. Coincidentally, Melusine was often thought of as a "White Lady," or Le Dames Blanches in French, which were female fairies that lived near streams and bridges in the Normandy area. They were thought to be extremely beautiful and possessing the gift of death foresight.
This tale is very similar to that of Lamia and makes me wonder if every European culture had their own version of this tale. Other notable mentions: Martin Luther called her a succubus, and meluzina in Czech refers to a gust of wind heard through the chimney, said to be the wailing of Melusina looking for her children. Many believe Melusine in medieval legend represented the idea of female sexuality and woman's dual-nature.
Julius Hubner - Melusine
The legend above was so influential that it became connected to Luxembourg through Guy de Lusignon, and in 1997 Luxembourg issued a postage stamp for her. (A few very powerful royals have tried to claim Melusine was their real-life ancestor, including Eleanor of Aquitaine, being that she descended from Raymond of Poitou's line.) In fact, the name Melusine may come from mere lusigne, meaning "mother of the Lusignans," although some believe it came from the Latin mal lucina, meaning "dark light," possibly in reference to Juno, which would make the siren-fairy-mermaid older than medieval times or at least connect Melusine to similar Greek and Roman myths - perhaps Lamia or the sirens. This might also be why Melusine is sometimes connected to the twin-tailed mermaid or alchemical siren.
Additionally, there is the Tour Melusine in Vouvant, the keep of a former castle of the Lords of Lusignan, that locals believed was truly built by Melusine.
One story that seems like an early version of Melusine's tale is that of Hippocrate's daughter. She was transformed into a dragon/giant serpant by the goddess Diana, then set to rule over an old castle. If a brave knight were to kiss her on any of the three days of the year she comes outside, she would then turn back into her rightful body. Alas, this never happens for her. The story is written in The Travels of Sir John Mandeville.
Other than the myths, there was Countess Petronilla Melusina von der Schulenburg of Walsingham, the illegitimate daughter of Ehrengard Melusine, Baroness von der Schulenburg, Duchess of Kendal and Munster, Princess of Eberstein (among other titles). She was the mistress of King George I of Great Britain. It is widely believed her middle name of Melusine was given in reference to the Melusine legends. Petronilla was named for her grandmother Petronelle Oddie de Schwenken. Besides Petronilla Melusina, Ehrengard Melusine also had two other daughters, Anna Luise Sophie and Margaret Gertrude. King George did have a wife, Sophia, whom he had two daughters with, but they both preferred the attention of others. After Sophia's lover was murdered for fear of scandal, their marriage was dissolved, and Sophia was imprisoned for more than thirty years until she died. It is unfortunate to know he merely died of a stroke at 67.
Melusina Fay Peirce, known as "Zina" but born Harriet Melusina Fay, was an activist and feminist born in Vermont. She also wrote, taught, and led initiatives for street cleaning and historic preservation. Today, Melusine Mayance is a French actress born 1999. There aren't too many real-life namesakes.
There is also a main belt asteroid named 373 Melusina (as almost all things in space are named after mythological figures or Shakespearean characters), a Belgian comic book, a song called "Melusine" by a metal band called Leaves' Eyes, one by the band Lilys, and one by Nolwenn Leroy, an animation company called Melusine Productions, a 1971 German opera titled Melusine, and quite a few literary references, including Melusine by Sarah Monette, Lady of the Rivers by Phillipa Gregory, The Fair Melusina by Felix Mendelssohn, The New Melusine by Goethe, The Wandering Unicorn by Manuel Mujica Lainez, and Possession by A.S. Byatt.
But, wait! There's more. Because of her closeness to other watery fantasy creatures, Melusine has been a character in Undine by Friedrich de la Motte, La Magicienne by Halevy, Ondine by Jean Giraudoux, a poem titled Melusine by Georg Trakl and one by Letitia Landon, and the opera Rusalka by Antonin Dvorak.
Here are some extra sources.
Melusine by Maxine Gadd
This might have been my longest post so far, so I'll end it by suggesting that spelling the name Melusine or Melusina is a personal choice and that there would be little difference in getting your point across - the connection to the legends would still be obviously recognizable, and both have been used countless times without too much favor falling on one or the other. There were no babies born in 2010 or 2011 named Melusine or Melusina. Also, there's a little more information and pictures if you hunt for it.