Marisa cornuarietis, common name the Colombian ramshorn apple snail, is a species of large freshwater snail with an operculum, an aquatic gastropod mollusc in the family Ampullariidae, the apple snail family. These snails are popular in aquariums, and are also used in the wild as a biological control agent.
It is widespread in northern South America, although the type locality is unknown. The giant ramshorn snail is native to northern South America and Central America, including Bolivia, Brazil, Colombia, Costa Rica, French Guiana, Guyana, Panama, Suriname, Trinidad and Tobago and Venezuela.
Marisa cornuarietis was first discovered in the US in Coral Gables, Florida, in 1957. It has spread to many other counties in southern Florida. It was first found in Texas in 1983 and has also been reported in California and Idaho. This species has been introduced and has established itself in Florida, in the southeastern United States. Established populations of this snail now exist in Broward, Dade, Monroe, and Palm Beach counties. The initial introductions were probably from aquarium release, aka «aquarium dumping».
Although Marisa snails superficially resemble the great ramshorn snail because of the planispiral coiling of their shells, they are not at all closely related to true ramshorn snails in the family Planorbidae.
This is an easily recognizable species: the shell is flat-coiled (planispiral). The shell colour varies from pale to darker red or brown or more vivid shades of those colours and is fairly often striped. The shell diameter is usually 35 – 50 mm (2 in) or even larger.
Easily adaptable to captivity, this snail may invade and damage aquarium vegetation. It is practically omnivorous, and feeds on animal and vegetal detritus. This snail acts as a useful aquarium scavenger when it is not excessively numerous. Studies revealed that this species retards the growth of water hyacinths by feeding on the roots of the plants. It has been suggested that the snail be used as weed-control agent in the canals of south Florida.
Marisa cornuarietis is usually purchased intentionally from pet stores, whereas true ramshorn snails (family Planorbidae) are very often considered to be aquarium pests, acquired accidentally, clinging to leaves of aquatic plants.