Lineus longissimus

The bootlace worm (Lineus longissimus) is a species of ribbon worm and one of the longest known animals, with specimens typically measuring 5–15 m (16–49 ft), and individuals known to measure up to 30 m (98 ft) long. There exist reports claiming lengths of up to 55 m (180 ft), although it is possible that these are reporting individuals that have been stretched beyond their usual length. Its mucus is highly toxic.