Lineus longissimus

The bootlace worm (Lineus longissimus) is a species of ribbon worm and one of the longest known animals, with specimens up to 55 m long being reported. Its mucus is highly toxic.

Taxonomy
The bootlace worm is in the phylum Nemertea or ribbon worms. It is the most common nemertean found along the coasts of Britain.

Description
Bootlace worms may grow very long but are usually only 5 to 10 mm 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, reminiscent 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, William M'Intosh described a specimen that had washed ashore in the aftermath of a severe storm by St Andrews, Scotland, which was more than 55 m 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.

Habitat
Lineus longissimus can be found on Norway's and Britain's coasts, on the Danish east coast and also on Sweden's west coast.