The Slipper Shell, or in the case of this paper the Atlantic Slipper Shell Credula fornicata, lives most commonly in shallow subtidal sections of the ocean and is a type of snail. The slipper shell falls under the Phylum Mollusca, class Gastropoda (along with Whelks and Periwinkles), and subclass Prosobranchia.(Dando 1996) The Slipper Shell is known by a few other names such as Slipper Limpet, or Boat Shell. The reason they would get the name "Slipper," is because the inside of the shell resembles just that. There is an overlaying section inside the shell, which almost looks like a shelf where the organism once lived or still does live. This section of the shell, when the shell is turned upside down, looks like the section of a slipper where one would put their foot.
The Slipper Shell produces Calcium Carbonate which is what the actual shell is made up of. The Slipper Shell is roughly 2.5cm to 4cm in diameter. (Dando 1996)
The Atlantic Slipper Shell is a filter feeder, and unlike other limpets, which go out and graze on algae, the Atlantic Slipper Shell spends its full life span in the same spot. It has a suction creating foot, which allows it to attach to hard surfaces. It does not require a two-part shell because it uses whatever it is attached to as the other part in a way. The bottom side of the Atlantic Slipper Shell is never regularly exposed. It will attach to rocks, other Slipper Shells, and even other shelled organisms not of the same species. The Atlantic Slipper Shell is capable of covering an entire seabed in certain areas if the conditions are right (Dexter 1947). It also doesnt seem to have many predators which contributes to its success. These organisms have posed a problem off the coast of England, which will be discussed later in the paper.
The way in which the Atlantic Slipper Shells reproduce is quite extraordinary and efficient. They do mate directly as opposed to sending sperm and eggs into the water and hoping for a connection. Atlantic Slipper Shells tend to pile up, one on top of another and can make stacks of multiple Shells.
Because the Atlantic Slipper Shells are capable of changing sexes when necessary, the bottom shell in these stacks of shells is female and the top shells are male. The top shells directly fertilize this female at the bottom by sending down an extension to the female with sperm to fertilize the eggs. The larvae then sink to a point where they attach to more stacks of Slipper Shells, or they attach on their own to something else. If they attach to another stack of Slipper Shells, it remains a male. If it attaches on its own, it switches to a female, and tries to attract male Slipper Shells by secreting a chemical which does just that (Lilley). Another interesting fact is that when the bottom female Slipper dies, the next Slipper Shell up which is male, becomes female and this pattern is continued. Because the Slipper Shells are capable of changing sexes, there will always be an efficient ratio of males to females for reproduction.
Off of the coast of England, Slipper Shells pose a large problem for the Oyster population. The Slipper Shells will attach themselves with their suction like foot to the Shell of the Oysters and reproduce right on top of them. This will cause the Slipper Shells to start one of these stacks discussed above, right on top of the oysters. This is a threat to the oysters because both the Oyster and the Slipper Shells are filter feeders. If an oyster has a bunch of Slipper Shells growing all around it, the Slipper Shells will filter out all of the food before the food can reach the oyster. This will eventually starve the Oyster and it will die. If enough Slipper Shells grow on top of the Oysters, they also have the potential to crush the oysters and kill them directly. The situation with the Slipper Shells and the Oysters, is very similar to the situation in Lake Champlain with the Zebra Mussels and the Native Mussels.
The Slipper Shell, which can be considered a vital part of the ecology in certain areas, is also considered a problem in others. They are very efficient when it comes to feeding and reproducing, which makes them so abundant around the world in the oceans. There is not much potential for the population of these organisms to atrophy considering they have no significant predators.