The longest worm in the world is a species of marine worm known as Lineus longissimus, more commonly called the bootlace worm. It is a variety of ribbon worm and lives in shallow coastal waters near western Europe.
The record-breaking specimen was 180 feet long. That makes it more than just the world's longest worm; it's also considered the world's longest animal, according to Guinness World Records. It was discovered in 1884, washed up on the shores of St. Andrews following a severe storm. Most of its closest relatives in the group Nemertea are only a few inches long. The bootlace worm itself is not very large in terms of width, being only as thick as a strand of spaghetti.