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What is the Longest Animal?

Michael Anissimov
Michael Anissimov
Michael Anissimov
Michael Anissimov

The longest animal in the world is probably Lineus longissimus, the bootlace worm, in the phylum Nemertea, the ribbon worms. One specimen that washed up on the shore of St. Andrews, Scotland in 1864 measured 180 ft (55 m), almost twice as long as the longest blue whale on record, which measured 98 ft (29.9 m). Bootlace worms are long and thin, with a thickness of only 5-10 mm (0.5 - 1 cm). When handled, they produce large amounts of thick mucus with a faint pungent smell. The animal is brown with lighter longitudinal stripes. If folded up tightly, this record-setting longest animal would occupy a cube only about 17 cm (6.7 in) on a side.

Bootlace worms are free-living creatures which dwell on or in the sea floor, capturing prey with their proboscis. Often found among rocks, seaweeds, barnacle, or mussel beds or buried in sand or gravel substrates, bootlace worms are voracious predators. They wrap themselves around prey, such as crustaceans or annelids, which may be much larger than themselves, and stab it repeatedly with the stylet in their proboscis until the target is dead. If no other food is available, it is said that ribbon worms will consume themselves. They also secrete mucus from their proboscis to trap prey.

One bootlace worm was measured about twice that of the longest blue whale.
One bootlace worm was measured about twice that of the longest blue whale.

Other animals besides the bootlace worm have contended for the title of world's longest animal. One is the siphonophore, which looks and acts like a single organism but is actually a colony of very closely cooperating animals. Siphonophores are cnidarians, like jellyfish, and include the Portuguese Man o' War. Some siphonophores have been measured at 130 ft (39.6 m) in length. Like bootlace worms, they are long and thin, but their front end is led by two swimming bells. Unlike bootlace worms, they are free-swimmers rather than bottom-dwellers. Siphonophores are rarely considered the world's longest animal because they are colonial and the Scotland bootlace worm of 1864 was longer, though most bootlace worms are much shorter.

Other animals of the past which are now extinct may have contended for the title of longest animal, but as most soft-bodied animals never fossilize, the majority are lost forever. One dinosaur, Amphicoelias fragillimus, known only from fossils which have since crumbled to dust, may have been as long as 196 ft (60 m) in length, even longer than the bootlace worm, but this is merely conjectural, as no complete skeleton exists.

Frequently Asked Questions

What is the longest animal currently known to science?

The title of the longest animal goes to the bootlace worm (Lineus longissimus), which can reach lengths of up to 55 meters (180 feet), according to the Guinness World Records. These marine nemertean worms are found in coastal waters around the British Isles and are known for their incredible length and slim, ribbon-like appearance.

How does the bootlace worm compare to other long animals like the blue whale?

While the blue whale is the largest animal in terms of mass and volume, the bootlace worm surpasses it in length. Blue whales typically grow to about 30 meters (100 feet) long, making them the largest mammals, but they are still shorter than the maximum recorded length of the bootlace worm. The worm's slender form allows it to stretch out much longer than the more robustly built whale.

Are there any other marine animals that rival the length of the bootlace worm?

Another contender in the marine world is the lion's mane jellyfish (Cyanea capillata), which can have tentacles that extend up to 37 meters (120 feet). However, even the longest lion's mane jellyfish falls short of the bootlace worm's record. The worm's length remains unmatched among known marine animals.

What adaptations allow the bootlace worm to grow so long?

The bootlace worm's elongated body is an adaptation that likely aids in its survival, allowing it to navigate narrow crevices and complex seabed terrain. Its length could also be a defensive mechanism, as predators may find it difficult to consume such a long, slender creature in its entirety.

How do scientists measure the length of such long animals accurately?

Measuring extremely long animals like the bootlace worm involves careful observation and sometimes indirect methods. Scientists may use markers or tags along the animal's body and measure segments at a time, or they might rely on photographic evidence and comparisons with known objects or scales. In some cases, specimens are measured after they've washed ashore.

Are there any terrestrial animals that come close to the length of the bootlace worm?

On land, the reticulated python holds the record for the longest reptile, with individuals recorded at over 6.95 meters (22.8 feet) long. However, this is still significantly shorter than the bootlace worm. Among terrestrial animals, no known species approaches the extraordinary length of the bootlace worm.

Michael Anissimov
Michael Anissimov

Michael is a longtime AllThingsNature contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Learn more...
Michael Anissimov
Michael Anissimov

Michael is a longtime AllThingsNature contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Learn more...

Discussion Comments

musicshaman

Did you know that the longest cat in the world is thought to be 48 inches long. Now I know that's nowhere near as long as a bootlace worm, but still, for a cat, that's crazy long!

Charlie89

That is so gross! Now I never want to swim in the ocean again! Nice article though.

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    • One bootlace worm was measured about twice that of the longest blue whale.
      By: GrrlScientist
      One bootlace worm was measured about twice that of the longest blue whale.