Worldbuilding the Undersea
On special request from @galacticnightsky123, I wanted to go into more depth on my world building sources and inspirations than the replies section allows. Thank you so much for giving me the opportunity to elaborate!
When I was world-building for Twilight Tides, I knew what tone I was going for in the story. I wanted a really young YA that borders on middle grade for this concept, a slightly more-grown up version of Barbie: A Mermaid Tale or The Little Mermaid (1989). This world needed to feel fun and have feminine appeal, the kind that where a girl might read it and want to live in the Undersea. I wanted to add some additional esoteric, ethereal elements such as in Kingdom Hearts. These major directions shifted me in the direction of how I wanted to handle the magical peoples of the Undersea.
I knew also that I wanted to make the magical world have a lot of different cultures and groups for our protagonists to explore. Mainly this was to service the wonder of the Undersea and to add nuance to our "representative" characters of the mermaid world.
The first thing I do when world-building a fantasy race/culture or creature is I look up some general lore about the group. For example, with the mermaids I looked to Hans Christian Andersen's original story, older mermaid myths, and the stories that inspired him like the legend of Undine and the Melusina. From these, I was able to learn the lay of the land and then modify as I felt was fit.
For example, with the Selkies, I combined the general Irish myths with some of the imagery regarding the Inuit seal goddess Sedna, using the name of her realm for their lost island. However, I also chose to change them from a seal-coat as the source of their transformation to a talisman to suit my preferred aesthetics. That's also where the blue and silver hair came in!
The mermaids were a little more by-the-book for pop culture, with their music magic, traditional appearance, and penchant for tragic relationships with humans. Some innovations, like the culture being matriarchal, derived from the overwhelming tendency for the characters of this species in folklore and fiction to be female, as well as my finding the terms "merfolk" and similar to be a bit clunky. So it worked better for "mermaid" to be the default and from there, for the culture to be primarily matriarchal.
The sea-dragons took inspiration from a couple different sources, and are tied to the more Kingdom Hearts elements of the story. I was primarily inspired by Elizabeth Lim's The Dragon's Promise, Axie Oh's The Girl Who Fell Beneath the Sea, and the Vidyahara of Honkai Star Rail.
The Oceanids are the group that has the least to do with the mythological inspiration they were named for. A starting source of inspiration was Te Fiti as depicted in Moana, which in turn gave the idea for a dualistic spirit of the water with a lava and life-giving connotations. The dualism and the vengeance motif also overlapped with the usual folklore regarding water spirits, making it an interesting inspiration to work with.
All of these groups started with a root in various mythologies across the world, and by taking inspirations from different places and twisting them to my thematic/aesthetic preferences, I feel I've made something really interesting here, and I hope you all will agree.
A final note on some of the original questions goes to aging and lifespan. The mermaids have the initial development of a normal human (maturity in 18 years) but live for 300, as per Andersen's original text. Selkies are about the same.
Oceanids are a little more difficult to gauge, especially as they are so rare in the world of the Undersea, but they age more slowly and have a lifespan past 500, I'd say.
Dragons are hypothetically immortal, resembling LOTR elves in how they age and live, but circumstances have killed them off pretty much at this point. Living forever does mean that people develop a grudge or two, I suppose.
Thank you so much for your questions, and I hope that this clarifies a bit more about how I world-build and about the world of the Undersea!
