Mollusks of the Aura River Valley

What are mollusks? The scientific name of this group, Mollusca, gives a hint about its characteristics. The name comes from the Latin word mollis, meaning soft. Mollusks are a group of soft-bodied invertebrates. In Finland, there are 23 species of slugs, 73 species of snails, and about 35 species of mussels. Several of these species can be found in the Aura River Valley, but identifying them often requires practice, as they are not as familiar to many people as other species. Mollusks include both plant-eating species and those that decompose decaying organic matter.

One of Finland’s largest slug species is the large black slug. Its coloration ranges from black and grey to brown, and it can reach 10–20 cm in length. It has a noticeable ridge running along its back, most prominent near the rear. The large black slug is a forest-dwelling species but may also be found in sheltered areas of gardens. It is a beneficial native species and should not be confused with other large slugs, such as the invasive Spanish slug.

Snails are easily distinguished from slugs by their hard calcareous shells. Snails require large amounts of calcium to build their shells, which is why they thrive in calcareous soils. For this reason, many snail species inhabit deciduous woodlands, making the Aura River Valley an excellent environment for them. The grove snail is common in the area and prefers environments with abundant vegetation. Its shell is dark or reddish brown with irregular yellowish patches. In addition to land-dwelling mollusks, several snail species also live in the river, including Finland’s largest freshwater snail species, the river snail.

Several mussel species have also been recorded in the Aura River, the most notable being the endangered thick-shelled river mussel. The thick-shelled river mussel is strictly protected under EU legislation, and its important habitats must not be deliberately degraded or destroyed.

Did you know that slugs are hermaphrodites, meaning they possess both male and female reproductive organs?

More information on slugs, snails and mussels.