They live mostly in the shallow sections of the ocean. Here's what the NJ Sea Grant Consortium has to say about them.

The vacant shell of the Atlantic Slipper Snail is a common find along our shoreline. The creature that initially inhabits this shell is called a Slipper Snail because when the shell is empty and turned upside down, it looks very much like a bedroom slipper.

The Slipper Snail has to attach itself to something hard in order to protect itself, something like a rock, other Slipper Snails, or even another shelled critter. Turn over a piece of jetty rock or a fully-grown Horseshoe Crab, and odds are you'll find Slipper Snails hanging on. Atlantic Slipper Snails tend to pile up in stacks, one on top of another, to protect themselves.

The Slipper Snail doesn't have to hunt for food. It is a filter feeder, so it filters out small bits of food or plankton from the waters that surround it. It also doesn't have too many predators so that contributes to the species' overall success.

Unlike most other shelled creatures, which reproduce by sending eggs out into the water hoping for a connection (also known as the broadcast method) the Slipper Snail mates directly and is prolific. It can change sex at will! All Slipper Snails start off male, but because it is capable of changing gender, it can become female. So if there are too many males around, a quick-change to female will keep the species going so that it can reproduce!