Planorbarius corneus

The Great Ramshorn Snail, Planorbarius corneus, is a large European species of air-breathing freshwater snail. Often confused with its smaller relatives, this species can reach a significant size, with its shell diameter growing up to 40mm. Its coloration is typically reddish-brown, a result of having haemoglobin in its blood, which is an adaptation for surviving in low-oxygen environments. This physiological trait is complemented by its ability to breathe atmospheric air using a primitive lung, which is why they frequently visit the water's surface.

As an omnivore, P. corneus has a voracious appetite and serves as an effective detritivore, consuming leftover food, fish waste, and biofilm. However, its dietary habits are a double-edged sword for the aquarist. While they efficiently clean up debris, they are also known plant eaters, showing a preference for softer-leaved species like Cabomba or Limnophila. This makes them less ideal for delicate Dutch-style aquascapes but suitable for tanks with tougher plants like Anubias or Java Fern. For optimal health and strong shell growth, their diet should be supplemented with calcium-rich foods such as blanched vegetables (zucchini, spinach) or specialized snail wafers. This dietary need is directly linked to water chemistry; they thrive in neutral to alkaline water (pH 6.5-8.0) with moderate to high mineral content (90-300 ppm GH), as acidic, soft water will cause their shells to erode and become pitted.

Breeding is exceptionally straightforward, as these snails are hermaphrodites. While they typically engage in cross-fertilization, self-fertilization is possible, meaning a single snail can potentially start a new population. They lay transparent, gelatinous egg clutches on any available surface, including glass, decorations, and plant leaves. Each clutch contains dozens of eggs that hatch within a few weeks, depending on the temperature. This rapid reproductive rate can lead to population explosions, which can increase the bioload on the aquarium's filtration system. Aquarists often manage populations through controlled feeding, manual removal, or by introducing natural predators such as Assassin Snails (Clea helena) or certain loach species. Despite their potential to become a nuisance, their prolific nature makes them an excellent, sustainable live food source for pufferfish, larger cichlids, and loaches.

Planorbarius corneus is a large gastropod mollusc belonging to the family Planorbidae. A key morphological characteristic of this family is the planospiral shell, which coils in a single flat plane. While the shell appears sinistral (left-coiling), the animal's soft body is anatomically dextral, a condition known as pseudosinistrality. Adult specimens typically exhibit a shell diameter between 20 mm and 40 mm, making them one of the largest ramshorn species encountered in the aquarium trade.

Physiologically, P. corneus is exceptionally well-adapted to lentic (still or slow-moving) freshwater habitats, as reflected by its stated preference for low-flow environments. Its most notable adaptation is its bimodal respiratory system. It possesses a ctenidium (gill) for aquatic gas exchange, but this is supplemented by a highly vascularized pulmonary cavity (a lung) derived from the mantle cavity. This allows the snail to utilize atmospheric oxygen, granting it high survivability in hypoxic conditions. Another significant physiological trait is the presence of haemoglobin as its respiratory pigment, which imparts a reddish color to its blood and body tissues and increases oxygen-carrying efficiency, a trait uncommon among molluscs.

Reproductively, P. corneus is a simultaneous hermaphrodite, possessing both male and female reproductive organs. While protandry (maturing as male first) is common, they can function as both sexes concurrently, and both cross-fertilization and self-fertilization (automixis) are documented reproductive strategies. This reproductive flexibility contributes to its classification as an r-strategist, characterized by rapid population growth and colonization potential. Gelatinous egg masses are deposited on various submerged surfaces. In a closed aquatic system, its metabolism and feeding result in a medium waste output, corresponding to a bioload factor of approximately 2.0, which should be factored into nutrient load calculations for the aquarium. Its native range is across the Palearctic, and its widespread, stable population gives it an IUCN status of Least Concern (LC).