Ampullariidae (apple snail)

The family Ampullariidae - commonly referred to as apple snails - are large tropical and subtropical amphibious freshwater gastropod mollusks.
The Ampullariidae are peculiar because they have both gills and lungs, the mantle cavity being divided to separate the two types of respiratory structures.

Distribution
This family includes several genera. Asolene, Felipponea, Marisa, and Pomacea are New World genera (native to South America, Central America, the West Indies and the Southern U.S.A.). The genera Afropomus, Lanistes, and Saulea are found in Africa. The genus Pila is native to both Africa and Asia.

Importance to humans
Common aquarium pet
Apple snails are popular aquarium-pets because of their attractive appearance and size. When properly cared for, some apple snail species can reach 15 cm / 6 inch diameter. Apple snails are in fact the biggest living freshwater snails on earth.
The most common apple snail in aquarium shops is Pomacea bridgesii (spike-topped apple snail). This species comes in different colours from brown to albino or yellow and even blue, with or without banding. Another common apple snail is Pomacea canaliculata; this snail is bigger, rounder and is more likely to eat aquatic plants, which makes it less suitable for most aquaria. This species also come in different shell and body colours. The "giant ramshorn snail" (Marisa cornuarietis) although not always recognized as an apple snail due to its discoidal shape, is also a popular aquatic pet. Occasionally, the Florida apple snail (Pomacea paludosa) is found in the aquarium trade and these are often collected in the wild from ditches and ponds in Florida. The giant Pomacea maculata rarely finds its way into aquaria.
Apple snails are often sold under the name "golden (ivory, blue, black...) mystery snail" and they are given incorrect names like Ampullarius for the genus instead of Pomacea and wrong species names like gigas instead of maculata. These snails will "play dead" on occasion (especially when first introduced to a new tank, probably from the stress of moving from one habitat to another), even for several days, but once the snail is acclimated it will become a surprisingly active (albeit slow motion) participant in the community tank.

A pest
In the 1980s, Pomacea canaliculata was introduced in Taiwan to start an escargot industry (Halwart 1994). It was thought that such food culture could provide valuable proteins for farmers, who primarily live on a rice diet. However, the snails did not become a culinary success because the imported snails (like the native apple snail population, Pila) were able to transfer a parasite called Angiostrongylus cantonensis. This parasite can infect humans if snails are eaten which have not been cooked thoroughly.
Instead of becoming a valuable food source, the introduced snails escaped and became a serious threat to rice production and the native ecosystems. During the 1980s the introduced snails rapidly spread to Indonesia, Thailand, Cambodia (Jahn et al. 1998), Hong Kong, southern China, Japan and the Philippines, and there are indications that they are currently invading Australia.
Hawai'i experienced the same introduction of Pomacea for culinary purposes, and its taro industry is now suffering because of it.
Nevertheless, apple snails are considered a delicacy in several regions of the world, and they are often sold in East and Pacific Asian markets for consumption.

Bio-control
Pomacea and Marisa species have been introduced to Africa and Asia to control snails (Planorbidae: Bulinus sp. and Biophalaria sp.) that serve as an intermediate host for trematoda parasites. These parasites can cause swimmers itch and schistosomiasis, a disease that affects over 200 million people in tropical regions. One of the species introduced as bio-agent is Marisa cornuarietis. This snail competes with other snails and predates on other species. Hopefully Marisa will not develop into a pest as have the introduced Pomacea species in Asia.

http://en.wikipedia.org/wiki/Apple_snail