Gyraulus (Gyraulus ioanis)

GenusGyraulus (1)
SizeShell height: up to 1.3 mm (2)
Shell diameter: up to 4.7 mm (2)

Gyraulus ioanis is classified as Critically Endangered (CR) on the IUCN Red List (1).

Gyraulus ioanis is a small species of snail in the Planorbidae family, members of which have a shell that is disc-like and flattened in appearance (3). The shell of Gyraulus ioanis has three to four whorls, and is glossy to silky, and also transparent. Fine growth lines can be seen on the shell (2).

The body of Gyraulus ioanis is light grey and is marked with small black spots (2). Like other members of the Planorbidae family, Gyraulus ioanis has long and slender tentacles (4).

Gyraulus ioanis is endemic to Montenegro, where it occurs only in Šasko Lake (1).

Only occurring in the edge zone of Šasko Lake, Gyraulus ioanis inhabits floating and emergent vegetation (2).

As it is a rare, recently discovered species of aquatic snail, there is little available information on the biology of Gyraulus ioanis. However, members of the Planorbidae family are known to be hermaphroditic, with an individual snail possessing both male and female sexual organs (3). Planorbidae are pulmonates, meaning that they can breathe air, which enables some members of the family to survive generally unfavourable, low-oxygen conditions. Planorbidae species can also absorb oxygen directly from the water (3).

The diet of most Planorbidae species consists of plant matter, with some species feeding on fresh plants and algae, while others feed on decaying plant matter (3) (5).

The entire population of Gyraulus ioanis is restricted to a single, small lake, and is therefore highly vulnerable to alterations in its habitat. The lake is currently undergoing a process known as eutrophication, which results in the depletion of oxygen in the lake and the creation of unfavourable conditions for many organisms (1).

During the summer, the water level in Šasko Lake decreases due to the interruption in flow of the main river entering the lake. This drop in water level may also potentially threaten Gyraulus ioanis (1).

Although there are no known specific conservation actions in place for Gyraulus ioanis, monitoring of this species’ habitat is recommended as a future conservation measure (1).

Find out more about Gyraulus ioanis:

Find out more about species in the Mediterranean Basin:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (December, 2011)
  2. Glöer, P. and Pešić, V. (2007) Gyraulus meierbrooki, G. ioanis, and G. shasi - three new Gyraulus spp. from the Skadar Lake Basin, Montenegro (Gastropoda: Planorbidae). Mollusca, 25(2): 131-137. Available at:
  3. Baker, F.C. (1945) The Molluscan Family Planorbidae. The University of Illinois Press, Urbana.
  4. Brown, D. (2005) Freshwater Snails of Africa and their Medical Importance. Taylor & Francis, London.
  5. Recknadel, F. (Ed.) (2003) Ecological Informatics: Understanding Ecology by Biologically-Inspired Computation. Springer, Berlin and Heidelberg.