Bootlace worms may grow very long but are usually only 5 to 10 millimetres (0.20 to 0.39 in) in width. The body is brown with lighter (longitudinal) stripes. Its mucus contains a relatively strong neurotoxin which it uses as a defense against predators. When handled it produces large amounts of thick mucus with a faint pungent smell, reminisscent of iron or sewage. This toxic mucus has been shown to kill crabs and cockroaches, and could have applications as an agricultural insecticide.
In 1864 a specimen washed ashore in the aftermath of a severe storm by St Andrews, Scotland, which was more than 55 m (180 ft) long, longer than the longest known Lion's mane jellyfish, the animal which is often considered to be the longest in the world. However records of extreme length should be taken with caution, because the bodies of nemerteans are flexible and can easily stretch to much more than their usual length.
Like other nemerteans, Lineus longissimus feeds using its eversible proboscis. As it is in the class Anopla, its proboscis is not armed with a barbed stylet. Instead it has a cluster of sticky filaments at the end of its proboscis that it uses to immobilize prey.
Lineus longissimus can be found on sandy shores, muddy shores, and in tide pools.
- "Potential insecticide discovered in Earth's longest animal". UQ News. Retrieved 2018-03-30.
- Strand, M., Sundberg, P. 2010. Lineus longissimus Långsnöre, p. 104 - In: Nationalnyckeln till Sveriges flora och fauna. Stjärnmaskar - slemmaskar. Sipuncula - Nemertea. Artdatabanken, SLU, Uppsala, ISBN 978-91-88506-72-6
- "MarLIN - The Marine Life Information Network - Bootlace worm (Lineus longissimus)". www.marlin.ac.uk. Retrieved 2018-03-30.
- Milius, Susan (2018-03-30). "Toxins from the world's longest animal can kill cockroaches". Science News. Retrieved 2018-03-30.
- "Insect toxin detected in the world's longest animal". ScienceDaily. Retrieved 2018-03-30.
- Carwardine, M. 1995. The Guinness Book of Animal Records. Guinness Publishing. p. 232.
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