Body narrow, head small and not much broader than the neck. Hooks 7-9, colourless and with a curved tip, serrated in juveniles. One pair of lateral fins, beginning at the level of the ventral ganglion onto about one third of the tail segment. Fins are partially rayed. No collarette and alimentary diverticula. Gut colourless, with oil droplets. Eyes not pigmented. Teeth 2-26, short and in one row.
Ovaries narrow, reaching to about half the length of the trunk; ova rather small. Developing eggs are carried in marsupial (brood) sacs, that hang each side from the opening of the oviduct. Seminal vesicles elongated, close to lateral fins.
Maximum body length 43 mm, relative tail length 19-25%.
Distribution in the North Sea
All North Sea (Off North Scotland, North East Atlantic).
Epi- to bathypelagic, regulated by temperature.
Bipolar distribution with tropical submergence: epipelagic in high latitudes, meso- to bathypelagic at low latitudes.
[After Pierrot-Bults and Chidgey, 1988]