Astacus astacus, commonly known as the European crayfish, is a freshwater crustacean found in rivers, lakes, and streams across Europe. It has a robust body, typically measuring 10 to 15 centimeters in length, and is characterized by its large claws and a dark green to brown coloration. This species prefers clean, well-oxygenated waters and is often found hiding under rocks or in burrows. The European crayfish plays a vital role in its ecosystem, serving as both predator and prey. It feeds on a variety of organic materials, including plants, insects, and detritus. However, Astacus astacus populations have been threatened by habitat loss and the introduction of non-native species, such as the signal crayfish (Pacifastacus leniusculus), which carry diseases that can harm native populations.