Marisa cornuarietis, common name the Colombian Ramshorn Snail, is a species of large freshwater snail with an operculum, an aquatic gastropod mollusc in the family Ampullariidae. It is widespread in northern South America and Central America, including Bolivia, Brazil, Colombia, Costa Rica, French Guiana, Guyana, Panama, Suriname, Trinidad and Tobago and Venezuela. These snails are popular in aquariums, and are also used in the wild as a biological control agent.
Marisa cornuarietis lives in lakes, ponds, irrigation systems and swamps. These snails stays close to the surface and prefer shallow waters with a lot of vegetation. They are known to tolerate relatively high salt concentrations and they are occasionally found in light brackish-waters. They are able to survive in these brackish waters, but they do not reproduce under these conditions. It’s reported that Marisa cornuarietis can withstand a salinity up to about 30% salt water. In general, the temperature may not drop below 12°C for prolonged periods for these snails to survive. The recommended water parameters: temperature 20°C – 26°C, water hardness 3 – 15 dGH, acidity pH 6.0 – 7.5.
Although Marisa cornuarietis superficially resemble the great ramshorn snail because of the planispiral coiling of their shells (3.5 – 4 whorls), 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 color varies from pale to darker red or brown or more vivid shades of those colors, and is fairly often striped. The 3 to 6 dark spiral bands are not present on the spine of the shell, but are mainly located at the umbilicus. The result of this unequal-banding pattern is that these snails often have a yellow and a black side. A mutation, in which the banding pattern is absent, exists. These snails have a completely yellow shell. Older snails have a planorboid shell (the spine isn’t elevated above the body whorls, making the shell almost flat). Young snails have an elevated spine, making them globose-shaped. The adult snail’s shell is about 18 – 22 mm wide and 48 – 56 mm high or even larger; pronounced growth lines (transverse stria) on adult shells near the aperture; aperture plane makes a slight angle with the shell axis (10°). The thin operculum is smaller than the shell opening and can thus be retracted completely into the shell. This species has gills as well as a lung, to ensure efficient underwater respiration even in condition of low levels of dissolved oxygen.
These snails eat almost everything they can get (omnivores): dead and rotting plants, many types of fresh plants, dead animals, eggs of other animals; voracious eaters. Not suited for planted aquaria. Marisa cornuarietis is a non-hermaphrodite, it lays eggs in characteristic disk-shape clutches, adhering to various substrates. Unlike some other Ampullariidae snails, this snail lays its eggs below the waterline. The size of the eggs is about 2 to 3 mm when deposited. The eggs are visible as small white spots inside the transparant gelatinous mass that surrounds them. During the development of the little snails, the eggs swell considerable (up to 4 mm). They also become more transparant and the little snails become visible as little spots attached at the inside wall of each egg.