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Giant ramshorn snail

Marisa cornuarietis

The Giant Ramshorn Snail is a massive, voracious freshwater gastropod. While an excellent scavenger, it will rapidly consume live aquatic plants.

Taxonomy
Class:Gastropoda
Order:Architaenioglossa
Family:Ampullariidae
Genus:Marisa
Species:Marisa cornuarietis

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Water Temperature

20 - 28 °C

pH Value

7 - 8.4

Water type

Freshwater

Invertebrate type

Freshwater snail

Adult size

4 cm

Minimum group

>= 1

GH

6 - 20 dGH

KH

3 - 15 dKH

TDS

120 - 450 ppm

Ecological role

Scavenger

Copper sensitivity

High

Species description

Geographical Origin and Habitat: The Giant Ramshorn Snail (*Marisa cornuarietis*) is a massive aquatic gastropod natively endemic to the warm, slow-moving rivers, expansive swamps, flooded plains, and highly vegetated lakes of Central and South America (specifically Colombia, Venezuela, Panama, and parts of Brazil). Their natural biotope is defined by incredibly dense stands of submerged and floating aquatic vegetation in still, nutrient-rich, and highly alkaline waters, where they function as apex macroscopic herbivores.
Taxonomy: Scientifically, their common name is a massive deception: they are NOT true Ramshorn snails (family Planorbidae), but are actually closely related to the giant Apple Snails (family Ampullariidae). Fully mature adults reach a staggering 3.5 to 5.0 centimeters (1.4-2.0 inches) in diameter. Unlike other Apple Snails that possess a conical spire, their massive calcium-carbonate shell is coiled flat in a "planispiral" shape (like a Ramshorn). Like Apple Snails, they possess gills, a lung, an extendable breathing siphon, and an operculum (trapdoor).
Social Behavior: They are peaceful toward fish but function as unstoppable, bulldozing biological terrors to aquatic vegetation. They are massive, highly active, and voracious scavengers. Due to their immense weight, they spend most of their time prowling the substrate or heavy hardscapes. However, utilizing their lung, they will frequently climb the aquarium glass, extend their siphon tube above the waterline to inhale atmospheric air, and drop heavily back down to the bottom.
Coloration and Sexual Dimorphism: Unlike true Ramshorns, which are hermaphrodites, the Giant Ramshorn possesses distinct sexes. Sexual dimorphism is visible to the trained eye: males generally possess a pale white or cream-colored foot, while females possess a dark brown or black foot. The massive, deeply grooved shell features a pale yellow, golden, or cream base, heavily overlaid with highly distinct, thick, dark brown or almost black longitudinal stripes that run entirely around the spiraled shell.

Care, breeding and tankmates

Tank Setup: The aquarium architecture MUST flawlessly accommodate their immense adult size, heavy waste output, and absolute destruction of vegetation. A minimum 75-liter (20-gallon) tank is mandatory for a single adult.
CRITICAL WARNING: You CANNOT keep this snail in a planted aquarium. They will completely obliterate and consume every single living plant, right down to the roots, within days. The tank MUST feature only heavy driftwood, massive rocks, or artificial plants. A tight lid with a 2-inch air gap is mandatory for them to breathe.
Diet and Feeding: They are ravenous, uncompromising herbivores and macrophyte (plant) eaters. In a bare aquarium, their massive appetite MUST be heavily fueled daily to prevent starvation. They MUST be fed massive quantities of fresh, calcium-rich vegetables (entire blanched zucchini halves, whole romaine lettuce leaves, spinach) and dozens of heavy sinking algae wafers every single day. They are not mere cleanup crews; their daily feeding requirements are equivalent to a large Plecostomus.
Water Quality: Originating from the dense swamps of South America, they thrive in standard tropical heat (22-28°C / 72-82°F). However, their massive size and ravenous appetite mean they produce an unbelievable amount of physical waste. Flawless, over-engineered filtration, combined with heavy weekly water changes, is unconditionally mandatory to prevent lethal Ammonia spikes. They strictly require hard, highly alkaline water (GH 8-20, pH 7.5 - 8.5) rich in dissolved calcium to maintain their massive shells.
Compatibility and Tankmates: Compatibility requires extreme care. While peaceful toward fish, they are massive, clumsy bulldozers that will crush small fry or delicate bottom-dwellers. They MUST NEVER be housed with aggressive, snail-crushing Cichlids or massive Loaches. Furthermore, because they are so voracious, they have been known to eat the eggs of other snails and fish. Excellent companions include fast-swimming schooling fish (Tetras, Barbs) and large, robust bottom-dwellers (Plecos, large Corydoras) in a bare or rocky tank.
Aquarium Breeding: Breeding is incredibly prolific and highly destructive if released into the wild (they are an invasive species in many regions). Unlike Apple Snails that lay hard pink eggs above the waterline, the Giant Ramshorn lays massive, gelatinous, transparent clutches of eggs completely underwater, attached to rocks, glass, or driftwood. These massive, jelly-like masses contain dozens to hundreds of eggs. If the clutches are not removed, hundreds of ravenous, plant-eating babies will overrun the tank.
Risks and Diseases: The absolute greatest physical risk is agonizing death from massive shell degradation caused by keeping them in soft, acidic water lacking calcium; extremely hard, highly alkaline water is unconditionally mandatory. The second major risk is massive, lethal water fouling (Ammonia spikes) if industrial-grade filtration is not utilized to handle their immense physical waste. Finally, releasing them into local waterways is highly illegal and ecologically devastating.

Geographic Origin and Distribution

The Giant Ramshorn Snail (*Marisa cornuarietis*) is a massive aquatic gastropod natively endemic to the warm, slow-moving rivers, expansive swamps, flooded plains, and highly vegetated lakes of Central and South America (specifically Colombia, Venezuela, Panama, and parts of Brazil). Their natural biotope is defined by incredibly dense stands of submerged and floating aquatic vegetation in still, nutrient-rich, and highly alkaline waters, where they function as apex macroscopic herbivores.

Origin

Amazon, Orinoco, and GuianasCentral America and CaribbeanNorth America

Invertebrate profile

Diet
Biofilm grazer
The diet of Marisa cornuarietis must be carefully managed to ensure robust health, vibrant coloration, and long-term survival in captivity. In its natural environment, it has specific foraging habits that should be replicated as closely as possible in the aquarium. Supplementing its diet with high-quality, targeted commercial foods or fresh preparations ensures it receives necessary vitamins and minerals. Care should be taken not to overfeed, as uneaten food will quickly degrade water quality and harm the animal.
Ecological role
Scavenger
Within its native ecosystem, Marisa cornuarietis plays a vital biological role that contributes to the overall stability of the environment. Whether acting as a scavenger, filter feeder, predator, or prey, it helps to efficiently cycle nutrients through the food web. Its natural behaviors prevent the over-accumulation of organic waste or the unchecked growth of specific prey populations. Introducing this species to a home aquarium often replicates these beneficial ecological functions, promoting a cleaner and more balanced system.
Shock sensitivity
High
Aquarists must be aware that Marisa cornuarietis is exceptionally sensitive to rapid fluctuations in its surrounding water parameters. Sudden shifts in temperature, specific gravity, pH, or dissolved organics can induce severe physiological shock, leading to rapid decline or death. A prolonged and careful drip acclimation process is highly recommended whenever moving this animal between systems. Maintaining pristine and unwavering water conditions is arguably the single most critical factor for its successful husbandry.
Calcium and minerals
High
Proper mineral balance is crucial for Marisa cornuarietis, as it requires consistent access to dissolved calcium and related trace elements for physiological maintenance. Depending on its specific biology, calcium is utilized for building external shells, hardening exoskeletons after molting, or supporting skeletal growth. In enclosed aquarium systems, these essential minerals can be rapidly depleted and may require regular supplementation. Routine water testing is encouraged to ensure that general hardness or specific calcium levels remain within the optimal range.
Molting
Shell growth
For invertebrate species that undergo ecdysis, Marisa cornuarietis requires a safe and stress-free environment to successfully shed its old exoskeleton. During and immediately following a molt, the animal's new shell is soft, leaving it extremely vulnerable to physical damage and predation. It is important to provide ample hiding spaces where it can retreat until its body fully hardens. If applicable, the discarded exoskeleton should be left in the tank, as the animal will often consume it to reclaim vital minerals.
Reproduction
Variable
The reproductive strategies of Marisa cornuarietis are varied and often highly adapted to its natural environmental conditions. Breeding efforts in a captive aquarium setting can range from straightforward to exceedingly difficult, often depending on specific larval requirements. Successful rearing of young frequently involves managing microscopic planktonic stages and specialized diets away from the main display tank. Nevertheless, captive propagation remains a rewarding endeavor that helps reduce the reliance on wild-caught specimens.
Compatibility & tankmates
Peaceful
Careful consideration of tank mates is required to ensure the safety and wellbeing of Marisa cornuarietis in a community setup. It should generally be housed with peaceful species that will not relentlessly harass it, nip at its appendages, or view it as a food source. Conversely, its own predatory or territorial instincts must be evaluated to ensure it does not harm smaller or slower-moving tank inhabitants. Observation during the initial introduction period is vital to confirm a harmonious balance within the aquarium.

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Last updated: 06/30/2026
Giant ramshorn snail (Marisa cornuarietis) Care Guide & Tank Setup | Atlarium