Clea helena (assassin snail)
This pretty species like to hide just under the substrate (we use aquatic sand for ours) and lie in wait for it's prey, mostly other water snails. Some people like to keep one or two of these in an aquatic tank to keep down the numbers of other snails.
Our assassins have also been fed on Hikari carnivore pellets when we are running low on smaller snails to keep with them.
Sold as juveniles at approx 1cm in size.