The bootlace worm is one of the longest known animals, with specimens up to 50 metres (164 ft) long and up to 10 centimetres (3.9 in) wide being reported. Its mucus is toxic.

Taxonomy

The bootlace worm is in the phylum Nemertea

Nemertea

Nemertea is a phylum of invertebrate animals also known as "ribbon worms" or "proboscis worms". Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than long, one specimen has been estimated at , which would make it the longest animal ever...

 or ribbon worms. It is the most common nemertean found along the coast

Coast

A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

s of Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

.

Description

They may grow as long as 60 metres (196.9 ft), which would make it the longest animal in the world. They are however usually only 5 to 10 mm (0.196850393700787 to 0.393700787401575 in) in width. The body is brown with lighter (longitudinal) stripes. Its mucus contains a relatively strong neurotoxin which it uses as a defence against predators.

When handled it produces large amounts of thick mucus with a faint pungent smell. A specimen washed ashore in the aftermath of a severe storm by St Andrews

St Andrews

St Andrews is a university town and former royal burgh on the east coast of Fife in Scotland. The town is named after Saint Andrew the Apostle.St Andrews has a population of 16,680, making this the fifth largest settlement in Fife....

, Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

, in 1864, had a length of more than 55 metres (180.4 ft), longer than the longest known Lion's mane jellyfish

Lion's mane jellyfish

The lion's mane jellyfish is the largest known species of jellyfish. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic, and northern Pacific Oceans, seldom found farther south than 42°N latitude. Similar jellyfish, which may be the same species, are known to inhabit...

, 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

Proboscis

A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

. As it is in the class Anopla, their proboscis is not armed with a barbed stylet. Instead they have a cluster of sticky filaments at the end of their proboscis that they use to immobilize prey.