Oscar-nominated writer-director Chris Sanders (“Lilo & Stitch,” “How to Train Your Dragon,” “The Croods”) has long had a fascination with mermaids, so when his wife, Jessica Steele-Sanders, suggested they collaborate on a book about the beguiling sea creatures, he, well, dove right in and “Rescue Sirens: The Search for the Atavist” was born.

The book follows the adventures of a team of young mermaids charged by an ancient vow to protect humans, so they masquerade on land as lifeguards in Miami Beach.

“We had always talked about the idea of mermaid lifeguards, but it really didn’t turn into something until I was standing in our living room and I heard sirens coming from the fire station down the street, and I thought, wait a minute: rescue sirens, lifeguard mermaids. And when I stopped laughing at my own corny joke, I said, hey, that’s actually a good title,” says Steele-Sanders. “It’s funny how when you name something, it becomes real. Once we had the name, I started coming up with the mythology behind it. So I pitched it to Chris.”

“I’ve always been looking for a mermaid story,” Sanders says, “So when she pitched that mythology, I was absolutely thrilled because there was such a simplicity to it, it clicked in my mind. I’m from animation, and in animation simplicity is strength. I thought, this is a great idea; it’s a very strong idea, so I said, all right. Let’s do this together”

After developing the mythology for about two years, Steele-Sanders, who grew up in Florida and worked as a lifeguard herself, among other ocean-related jobs, created an outline, then she and Sanders split up the writing, which they began in February. All the while, Sanders has been working on DreamWorks Animation’s “The Croods 2,” due out in 2017, and looking for a creative outlet during the long production process. A few short months later, the self-published books were selling at a brisk clip at Comic-Con.

“When you’re working on an animated film, it’s a monumentally slow process. Inevitably you’re looking for other things to do,” Sanders explains. “For me, this was a wonderful thing to partner with Jess on and feel that sense of completion. I’m very proud of it. When you’re finished and you send it to the printer and the binder and you get the actual book back, it’s an absolute thrill to see the finished product. And we were able to take it to Comic-Con, where we introduced it.”

In fact, the books, all of which are signed, sold so well at Comic-Con and online at RescueSirens.com that the authors have run out of their stock and plan to have more ready to sell in mid-August. But for those who don’t want to wait, there is a Kindle edition available on Amazon.com.

Sanders and Steele-Sanders are looking to take the “Rescue Sirens” story further. “We have more stories laid out,” explains Sanders. “If you have good characters, you know it, because you start talking about other things they could be doing.”

“This is the origin story,” adds Steele-Sanders. “This is the point at which you want to jump off and say, ‘OK, now here are all the adventures they can go on in the next couple of books.’”

With covers drawn in Sanders’ recognizable style, and the book’s richness in detail, it seems tailor-made for some sort of adaptation to the big- or smallscreen. “In fact, we would talk all the time about a TV series, because there are just so many things for them to do,” says Sanders. “I sat down one day and storyboarded the opening to the TV show. It’s something we’d talked about over and over again, so I said, ‘I’m just going to get it out.’”

Steele-Sanders notes how people assumed it was already a film or series when they first introduced the book on Facebook. “People would ask, “Is it a movie? Is it a TV series. Can I watch this on Netflix?”

“I think it definitely has that vibe,” adds Sanders. “It has everything it needs to launch into more stories.”