I never heard of it, but I googled it and came across a couple of different things, but both refer to a description of how it looks, not any species of wood. I’m not counting the results for actual tortoise shell, although I did see a couple results for inlays using tortoise shell. I’m guessing those would be pretty expensive antiques and if that’s the case, better to send it off to someone that knows what they’re doing.
Anyway, some of the results were wood grain patterns that look like turtle shell pattern. If that’s the case, you should be able to sand of the old finish. Although, be careful you don’t sand through veneers, if there are any.
The other group of results had to do with paint to mimic turtle shell pattern. If it’s painted, obviously you can’t sand it off or you would destroy the existing look. But if the paint is covered with varnish you might be able to lightly sand it and touch up the finish.
Losing fingers since 1969