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

Ramshorn snail

The term ramshorn snail is used in the aquarium trade to describe any kind of snail whose shell is planispiral, meaning that it is a flat coil. Such shells resemble a coil of rope, or (as the name suggests) a ram's horn.

Physical description
Most of these snails are of the family Planorbidae. Their blood, like human blood–contains hemoglobin, which may lend these snails a bright reddish color. These ramshorn snails breathe air. Although most are extremely small, some may reach a size of two and a half centimeters (one inch). The shells range from translucent through various shades of brown to a dark, nearly black color. The dark color appears to originate from dietary materials not generally available in the home aquarium, although many varieties from ponds will be this dark shade.
Snails of this family are spiralled sinistrally, with the opening hole slanted downward toward the right. Large folds of skin, which serve as primitive gills may protrude out of the more open left side. The shell contains no operculum, and the snail has only one pair of tentacles.
They lay eggs in globules, which tend to be brownish in color. The globules contain about a dozen or so eggs, though it can vary. The globules are translucent, so it is possible to visually see the new snails develop in size. The newborn snails are clearish white.

Interaction with environment
Ramshorn snails generally will eat only the most delicate plants, preferring algae, uneaten fish food, and dead fish. Some varieties do particularly enjoy eating the leaves of stem plants such as cabomba and anacharis.
Some aquarium species will eat ramshorn snails. More voracious eaters include loaches (such as the clown loach or any other member of the genus botia), bettas, crayfish, and most gouramis—though many other fish will also consume snail meat. The larger apple snail will also prey upon ramshorn snails.
Good fish roommates for snails include, but are not limited to, danios, guppies, White Cloud Mountain Minnows, neon tetras, and cory catfish. All of these are non-aggressive fish that cohabitate easily with snails.
One should also be aware that red ramshorn snails are able to carry various parasitic flukes, which can be transmitted to fish, or humans. Most of these flukes require intermediate hosts, so that leaving the snails by themselves for a month or so will eliminate the disease.

Role as aquarium pest
Most ramshorn snails are considered minor aquarium pests. They may arrive in a tank as egg bundles hidden in newly acquired plants. Although their red color may make them somewhat interesting aquarium subjects, their hermaphroditic ability to breed prolifically from any two specimens can make them troublesome.
Common practices include treating plants to prevent introduction, various manual methods of control, introducing the snail eating animals listed earlier, and poisoning the snails.
Soaking the plants in various chemicals may kill off the snails and their eggs. A 10 minute bath in a solution of 20 parts water to 1 part chlorine bleach has been suggested for hardier plants, followed by soaking in water containing a dechlorinating agent. A more gentle treatment calls for 5-10 tablespoons of alum to 1 gallon of water for 2-3 days. A safer alternative may be placing the plants in a quarantine tank, and adding snail poisons to that tank rather than the main show tank.
Manual methods include baiting the snails with lettuce, cucumber slices, or food pellets. These may be left out in the open, and removed with their snails, or kept in some container, such as a film canister weighed down with a pebble, and containing holes drilled in it. Crushing the snails by hand as they appear can also effectively limit their population; most ramshorn shells are fragile enough that this is quite easily done.
Snail poisons are generally considered to be a last resort, as most of them are copper based and potentially toxic to plants and fish. Even new safer chemicals that do not harm the other aquarium inhabitants may cause damage if large numbers of dead snails are allowed to decompose. For this reason, it is best to reduce the snail population by other means as much as possible before resorting to poisons, and to do frequent water changes afterwards. Some also recommend adding ammonium protection to the tank. Zeolite chips, and various liquid products such as amquel may help in this area.

Eponymous snails
Totally unrelated to these ramshorn snails is the species Marisa cornuarietis, which is often sold at pet stores under the name Columbian Ramshorn or Giant Ramshorn snail. This species is actually a type of apple snail. It is distinguished by having two pairs of tentacles, an operculum, and a siphon on the left side. Its shell is yellowish, with brown stripes running the length of the shell. These apple snails lay gelatinous masses of eggs on submerged portions of plants. Apple snails can grow to up to four centimeters in size. They generally will not become a pest, although they can consume large amounts of plant matter.

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