Capable of great extension and contraction. Individuals may extend themselves until they resemble a very fine thread, but if disturbed, may quickly coil themselves into a closely wound spiral.

(from Coe, 1904) Usually pale yellow throughout but some specimens have a distinct reddish tinge. Others may be grey, greenish, or pale green. A median pale line appears on the dorsal surface in the region of the esophagus. This is a very slender thread-like species. Body is commonly thicker in the middle and tapers toward both head and tail. Head is very long and sharply pointed when extended. Proboscis pore is ventral and farther back from the tip of the snouth. The mouth is very far back.

Eyes are absent in adults although embryos have a single pair soon after they leave the egg.

Can extend 3-6 inches but can contract to a fraction of this length.

Very common at high water mark under stones and in muddy places, among decaying mussels, etc. The worms were commonly found in black, slimy, and very foul mud.

Common on the coast of New England, shores of northern Europe, Mediterranean, Pacific coast of USA (Alaska)

They are often associated with reddish nematodes.