Okay. And you can't work them in? Why not?
@Remathilis gave multiple ideas of working in a turtle-race or a unique individual turtle person.
Sure, there are campaign themes where none of that would work . . . but very narrow campaign themes. But if you can find the players for your very specific and narrow campaign setting, that's great and everybody will likely have fun. But
@Remathilis will probably not be interested in your game. Neither would I. Are you okay with that?
It's not so much,
"Gosh darn, I was dead-set on playing a turtle-person!" but rather,
"Wow, this DM is really restrictive and prioritizes his worldbuilding over collaboration with players, and that's not a game I think I would be interested in." It's a red flag . . . not that you are a bad DM, but that your DMing style doesn't match what I'm looking for in a game.