Sometimes they can sometimes produce hybrids. They even may bear hybrid offspring. The hybrids of different species are usually sterile. However, lots of hybrids are fertile in a backcross. They can not bear offspring with another hybrid. read more
However, it has been shown in some species of snail. To form the hybrid to form a new species, there has to be lots of backcrosses. However, there is a problem when the parent species have different chiralities. read more
The only Apple snails that I've heard of cross breeding are Asolene Spixi, and Marisa (Giant ramshorns) You're most likely referring to Pomacea brigdesii as the mystery snail, and Pomacea canaliculata as the large apple snail, and these 2 species cannot cross breed. read more
some species can cross-breed, such as Cepaea nemoralis and Cepaea hortensis. Maybe you could take pictures of these aquatic snails and post them, and we might be able to identify them. read more