(Gunnerus, 1770)
Description:
This is the longest nemertean species known. Individuals of 5-10 m length are not uncommon. The species possesses a flaccid body which, when disturbed, contracts and extends in a series of irregular muscular waves. When handled the animals produce copious amounts of a rather viscid mucus which has faintly pungent odour. The colour ranges from a dark olive-brown or rich chocolate brown in younger individuals to a blackish-brown or black in larger animals. Often a flickering purplish iridescence is evident over the body surface which is due to the activity of the epidermal cilia. The body may appear streaked with pale longitudinal lines, especially on the anterior dorsal surface, and the lateral margins of individuals containing mature gonads have often a pale greenish-brown hue (L. longissimus). Ventrally the colour may be the same as or slightly paler than that of the dorsal surfaces. The cerebral ganglia show pink to red through the epidermis. The tip of the rectangular head is pale or whitish in colour and slightly bilobed (L. longissimus-head). There are 10-20 deep-set reddish-brown or black eyes arranged in a row on each side of the snout.
Habitat:
Probably the most frequently recorded of the British nemertean species, Lineus longissimus is typically found on the lower shore coiled into gently writhing knots beneath boulders on muddy sand, but also occurs in rock-pools, entangled among laminarian holdfasts, in rock fissures and clefts, or in deeper sublittoral locations on muddy, sandy, stony or shelly bottoms.
Distribution:
The geographic range of the species extends from Iceland eastwards to the Atlantic, North Sea and Baltic coasts of Europe, but it has not been found in the Mediterranean.