Description: An unsegmented worm with olive brown to black colouration that is usually streaked with purple or an iridescent sheen. There may be pale longitudinal lines visible. This worm is incredibly long, routinely measuring 5-15 m in length but has been recorded as being up to 30 m. There are 10-20 eyes near the head but they are normally not visible due to the dark colouration of the body.

Habitat: Found under rocks or muddy, sandy or shelly sediment from the lower shore to shallow sublittoral.

Distribution: Recorded from most coasts around Britain and Ireland, although there are no records from lower east coast.

Similar Species: Due to its length this worm is unlikely to be confused with any other species. There are other Lineus species present in Britain and Ireland, but anything over 1 m is likely to be Lineus longissimus.

Key Identification Features:

• Extremely long worm, 5-30 m in length.
• Olive brown to black colouration, often with purple or iridescent streaks.
• Pale longitudinal lines sometimes visible.

Distribution Map from NBN: Lineus longissimus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Lineus longissimus at iNaturalist World Species Observations database.

GBIF data for Lineus longissimus

WoRMS: Lineus longissimus at World Register of Marine Species. Accepted name: Lineus longissimus (Gunnerus, 1770). AphiaID: 122528.

Classification: Biota; Animalia; Nemertea; Pilidiophora; Heteronemertea; Lineidae; Lineus