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Swollen river mussel

Unio tumidus

Photo: Swollen river mussel
State of endangerment
Animal description
The Swollen River Mussel, scientifically known as Unio tumidus, is a species of freshwater bivalve belonging to the family Unionidae. This intriguing mollusk is found in rivers and streams across Europe and parts of Asia, thriving in environments that offer slow to moderate flowing waters with sandy or muddy bottoms.

Characterized by its distinctively thick and robust shell, the Swollen River Mussel can reach impressive sizes, typically measuring between 5 to 10 centimeters in length. The shell itself is somewhat oval or elliptical in shape, displaying a broad and tumid appearance that gives this species its common name. The exterior of the shell exhibits varying colors, ranging from dark brown to greenish or yellowish hues, often adorned with faint growth lines that add to its aesthetic appeal. The interior is smooth, with a nacreous layer that shines with an iridescent sheen, ranging from white to light purple.

One of the most fascinating aspects of the Swollen River Mussel is its complex life cycle, which involves a unique parasitic stage. Like many freshwater mussels, this species relies on fish to complete its reproductive cycle. The larvae, known as glochidia, are released into the water and must attach themselves to the gills or fins of a suitable fish host to develop. This symbiotic relationship allows the larvae to be dispersed to new locations as the host fish moves about in the water. After a period of development, the glochidia metamorphose into juvenile mussels and detach from the host, settling into the riverbed to continue their growth into adulthood.

The Swollen River Mussel plays a vital ecological role in its aquatic habitats. By filtering water as they feed, these mussels help to improve water quality, removing particles and pollutants from the environment. Furthermore, they serve as a food source for various predators, including fish, birds, and mammals, thus contributing to the biodiversity and health of their ecosystems.

Despite their importance, populations of the Swollen River Mussel have faced declines in recent years, primarily due to habitat destruction, pollution, and the impacts of invasive species. Conservation efforts are underway in many regions to protect and restore their habitats, aiming to ensure the survival of this remarkable species.

In summary, the Swollen River Mussel is a fascinating and ecologically significant freshwater bivalve, known for its robust shell, complex life cycle, and crucial role in aquatic ecosystems. Efforts to conserve this species and its habitat are essential for maintaining the health and biodiversity of freshwater environments.
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