What species is a turtle?

In scientific classification, "turtle" is an order, not a species (it's called "Testudines"). There are hundreds of species of turtles. The class of a turtle is Reptilia, meaning turtles are air-breathing reptiles. Common misconceptions are that turtles are amphibians, which they are not because they are reptiles, and that they have gills, which they don't because they breathe air.