apple snails and mystery snails are all different labels for the same thing, pomacea, the usual differences are Pomacea Diffusa, formerly known as Brigsii, are the more common. Generally not growing much more than a golf ball. Pomacea cana...nope, not even gonna try to spell the rest, are a slightly different species that can grow tennis ball size (but are usually at the end of life by the time they reach that impressive size!).
There are other species of pomacea, but are even rarer. Canas are notorious plant eaters, they destroy aquascaping. All apple snails will chow on blanched veggies, zucchini being the staple for mine.