Fabio Liverani / Freshwater Crab (Potamon fluviatile) in a shallow stream - split perspective showing crab beneath and fluvial habitat. Foreste Casentinesi National Park, Italy, July.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) brandishing claws in defensive posture. Foreste Casentinesi National Park, Italy, July.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) in a shallow stream - split perspective showing crab beneath and fluvial habitat. Foreste Casentinesi National Park, Italy, July.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) in a shallow stream - split perspective of underwater and habitat. Foreste Casentinesi National Park, Italy, July.

Fabio Liverani / Freshwater crab {Potamon fluviatile} in Resina river, Umbria, Italy

Fabio Liverani / Split level image of Freshwater crab {Potamon fluviatile} in Resina river, Umbria, Italy

Emanuele Biggi / Freshwater crab (Potamon fluviatile) living in old Roman ruins, Traiano's Market, Rome, Italy

Emanuele Biggi / Freshwater crab (Potamon fluviatile), mating pair, Italy, September.

Emanuele Biggi / Freshwater crab (Potamon fluviatile), adult female on stream bed at the entrance of her burrow, Italy. August.

Emanuele Biggi / Freshwater crab (Potamon fluviatile) adult female on stream bed at the entrance of her burrow, Italy. August 2012.

Emanuele Biggi / Freshwater crab (Potamon fluviatile), adult male at the entrance of its burrow, Tuscany, Italy, August.

Emanuele Biggi / Freshwater Crab (Potamon fluviatile), young carried in their mother's telson pouch, Tuscany, Italy. August.