Arno Atoll (Marshallese: Arņo, [ɑ̯ɑɳˠːʌ͡ɔɔ̯]) is a coral atoll of 133 islands in the Pacific Ocean, and forms a legislative district of the Ratak Chain of the Marshall Islands. Its total land area is only 5 square miles (13 km²). Unlike most other atolls, Arno encloses three different lagoons, a large central one, and two smaller ones in the north and east. Its main lagoon encloses an area of 130.77 square miles (338.7 km²).