This is the Great Ramshorn (Planorbarius corneus), a relatively large freshwater snail known for its coiled, disk‑like shell and role in pond and still‑water ecosystems. It grazes on algae and organic material and is widespread across much of Europe.

Location:
Planorbarius corneus is native to Europe, with a range extending from the British Isles and western Europe through central and southern Europe into the Caucasus and western Asia. It is found in still or slow‑flowing freshwater habitats and can sometimes be encountered outside its native range where released or introduced.

Average Size:
Adults commonly reach up to 3–4 centimetres in shell diameter, making them one of the larger species of ramshorn snails.

Family:
Planorbidae (Ramshorn Snails)

Species:
Planorbarius corneus

Shell Description:
The shell is coiled in a flat spiral, giving it a disc‑like appearance typical of ramshorn snails. It has typically 4–5 rounded whorls and is usually brown, olive or reddish in colour; lighter (albino) variants occur. The aperture (opening) is broad and nearly circular. Although the shell appears dextral (right‑coiling), like all planorbids it is technically sinistral (left‑coiling).

Habitat:
The Great Ramshorn snail inhabits still or slow‑moving freshwater such as ponds, lakes, ditches, canals and sluggish rivers, favouring waters rich in aquatic vegetation and dissolved minerals.

Feeding:
This species is a grazer and detritivore (feeds on dead organic material), using its radula (a tongue‑like organ with tiny teeth) to scrape algae from submerged surfaces and to consume decomposing plant and animal matter.

Movement and Behaviour:
Great Ramshorns are active throughout much of the year and may cling to submerged vegetation, stones or other structures. They are capable of breathing air when dissolved oxygen is low, thanks to a lung and the presence of hemoglobin in their blood, which helps them survive in low‑oxygen environments.

Reproduction:
Like many freshwater pulmonate snails, they are hermaphroditic, possessing both male and female reproductive organs. Egg masses are laid as gelatinous capsules attached to underwater plants, stones or other surfaces. Each capsule typically contains multiple eggs, and young snails hatch after a period depending on temperature and conditions.

Ecological Role:
As grazers and recyclers of organic matter, Great Ramshorn snails contribute to nutrient cycling in freshwater habitats. Their presence supports food webs and helps maintain water quality by controlling algal growth.

Conservation Status:
This species is classified as Least Concern and is common across much of its natural range. However, like many freshwater invertebrates, it can be sensitive to habitat degradation, pollution and changes in water quality.