Another relative of the snail is the slipper snail or Crepidula fornicata. The slipper snail, the white, mottled shell attached to the mussel in the image above, will attach to hard substrate in the water and spend their lives in that one place filtering food. Unlike a bivalve such as the clam or oyster, the slipper shell has just one shell with the a foot on the underside along with a shelf that extends about half the length of the shell. Slipper shells are very difficult to pry off a rock and attempting to do so often injures the animal. If a limpet is dislodged it can only attach to a substrate that is the shape of the one it grew up on, as the shell has taken the form or shape of its previous substrate.

Slipper snails are commonly found in stacks with a stack sometimes consisting of up to 12 animals. Reproduction is the main reason for these stacks to form. Large shells are found at the bottom of the chain, with the shells becoming progressively smaller towards the top. While all start as males, those that begin a stack change to female while those on top will most remain male. Female slipper shells produce about a hundred large yellow or orange eggs. Eggs are fertilized by the males on top of the stack. The eggs are kept inside the shell of the female, just in front of the foot, until they hatch. At hatching the tiny planktonic larvae are swept out of the shell.