White-clawed crayfish

White-clawed crayfish, Britain's only native freshwater crayfish, are under serious threat from an American invader. The introduced signal crayfish has had devastating effects, both out-competing the natives and carrying a deadly fungus against which the white-claw has no defence. Looking much like minature lobsters, they hide away under rocks and logs during the day, emerging at night to prey on larvae, snails and plants. Despite the threats, large populations can still be found in clean, well-oxygenated rivers and lakes across Europe.

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Worth watching the video of Bill Oddie and the Crayfish.

I remember the river Loddon being full of them in my childhood.