What Is the Smallest Octopus in the World
The smallest octopus in the world is typically recognized as the Atlantic pygmy octopus, also known as Octopus mercatoris. Adults of this species reach a mantle length of about 4 to 5 centimeters, with a total arm span often under 15 centimeters. It is a small benthic octopus found in the western Atlantic Ocean, including the Caribbean Sea and parts of the Gulf of Mexico. The species is noted for its compact body, short arms, and relatively simple behavior compared with larger octopus species. It is frequently cited in marine biology resources as one of the smallest known octopus species, alongside other pygmy and dwarf octopuses in the family Octopodidae. Learn more about small octopus species on Forbes.
Another very small octopus often mentioned in scientific literature is the East Pacific red octopus, or Octopus rubescens, which can have a mantle length close to 4 centimeters. In some regions, the day octopus and other small tropical species are also described as among the smallest octopuses, but the Atlantic pygmy octopus remains a primary reference for the smallest octopus in the world. These species are distinguished from larger octopuses by their reduced body size, fewer egg clutches, and shorter lifespans. Researchers use mantle length and total length measurements to compare octopus sizes across species. The smallest octopus in the world typically inhabits shallow coastal waters, seagrass beds, and coral rubble where it can hide from predators.
How Small Is the Smallest Octopus Compared With Other Species
Compared with the giant Pacific octopus, which can exceed 15 meters in arm span, the smallest octopus in the world is remarkably tiny. The Atlantic pygmy octopus has a mantle length roughly one-tenth of the giant Pacific octopus, and its total weight is often measured in grams rather than kilograms. Dwarf and pygmy octopuses in the family Octopodidae share traits such as small body size, reduced suckers, and a preference for crevices and small shells. Some species, like the coconut octopus, are slightly larger but still considered small relative to the giant species. The size difference highlights the wide range of body plans within the order Octopoda. View octopus size comparisons on Britannica.
Scientists measure octopus size using mantle length, the distance from the eyes to the tail, and total length, which includes the arms. For the smallest octopus in the world, mantle length is typically between 4 and 5 centimeters, and total length stays well under 20 centimeters. By contrast, the common octopus can have a mantle length of up to 25 centimeters or more. Egg size also scales with body size, and the smallest octopuses produce fewer, smaller eggs than their larger relatives. These measurements help marine biologists classify species and understand how body size affects survival, reproduction, and habitat use in different ocean environments.
Where the Smallest Octopus Lives and Why It Matters
The smallest octopus in the world is found in warm, shallow coastal waters of the western Atlantic, including the Caribbean Sea, the Bahamas, and parts of the Gulf of Mexico. It favors habitats with sandy or rubble bottoms, seagrass beds, and coral rubble where it can hide during the day. The Atlantic pygmy octopus is a nocturnal hunter, emerging at night to feed on small crustaceans, worms, and other invertebrates. Its small size allows it to occupy microhabitats and crevices that are inaccessible to larger