The natural world holds surprising extremes, often in creatures that rarely capture public attention. While large mammals or majestic birds might first come to mind, some of the most impressive records for sheer length belong to less visible organisms. These remarkable beings often live hidden in diverse environments, showcasing extraordinary adaptations to achieve their immense sizes.
The Nemertean Champion
The longest worm in the world is Lineus longissimus, commonly known as the bootlace worm. This species belongs to the phylum Nemertea, or ribbon worms. While typically measuring 5 to 15 meters (15 to 50 feet) long, an exceptional specimen found in St. Andrews, Scotland, in 1864, reportedly measured over 55 meters (180 feet), making it one of the longest animals ever recorded.
These slender worms are only 5 to 10 millimeters (0.20 to 0.39 inches) wide. Lineus longissimus inhabits the cold, shallow waters of the North Atlantic Ocean. They are found coiled beneath boulders, in muddy sand, or within rock crevices along the coasts of Norway, Britain, Denmark, and Sweden.
Beyond Length: Unpacking Its Biology
Lineus longissimus possesses several biological characteristics. Its body is dark brown to black, often marked with lighter longitudinal stripes on its anterior dorsal surface. The unsegmented body is covered in epidermal cilia, giving it a subtle purplish iridescence. This species exhibits elasticity, capable of stretching significantly and then contracting to a much smaller size.
As a carnivore, the bootlace worm preys on small invertebrates. It uses an evertible proboscis, a long, hollow tube shot out from an internal pouch to capture prey. For defense, Lineus longissimus produces thick, pungent mucus containing a neurotoxin called anabaseine. This toxic mucus deters predators, and its properties have been explored for use as an agricultural insecticide.
Other Giants of the Worm World
Other worm species also attain impressive sizes. The giant Gippsland earthworm (Megascolides australis) from Australia is one of the world’s largest earthworms, averaging 1 meter (3.3 feet) long and 2 centimeters (0.79 inches) in diameter. Some specimens reach up to 3 meters (9.8 feet) and live in deep burrow systems in blue-grey clay soils.
In the deep sea, the giant tube worm (Riftia pachyptila) grows up to 3 meters (9.8 feet) long with a diameter of 4 centimeters (1.6 inches). These marine invertebrates thrive near hydrothermal vents on the Pacific Ocean seafloor, relying on symbiotic bacteria for nutrition as they lack a mouth or digestive tract. Among parasitic worms, the broad or fish tapeworm (Diphyllobothrium latum) reaches 9.1 to 12.1 meters (30 to 40 feet) in humans, with some cases up to 18.28 meters (60 feet). Another tapeworm, Tetragonoporus calyptocephalus, found in whales, has been reported to reach 40 meters (131 feet).