The Leach's Spider Crab (Inachus phalangium), is a species of crab from the north-eastern Atlantic Ocean and Mediterranean Sea. It is up to 20.5 mm (0.81 in) wide.
Large males may reach a carapace size of 20.5 by 17.5 millimetres (0.8 ×0.7 in), and is brownish-yellow in colour. The carapace becomes narrower towards the front of the animal, and is often concealed by epibionts.
I. phalangium is found in the eastern Atlantic Ocean, from Norway in the north to West Africa and the Cape Verde islands in the south, and extending into the Mediterranean Sea. It lives at depths of 11–55 metres (40–180 ft).
Inachus phalangium lives commensally with the sea anemone Anemonia sulcata (Snakelocks Anemone). The crab gains protection from potential predators by sheltering beneath the anemone's stinging tentacles. The crab eats particles of food dropped by the sea anemone, and mucus from the surface of the anemone.