Body small and thin, firm and opaque. Head small. Hooks serrated. Two pairs of lateral fins, separated and rounded, with a small zone without rays. The anterior fins begin at the rear end of the ventral ganglion. Collarette very thin. No alimentary diverticula. Eyes small, with T-shaped pigment spot.
Ovaries reaching to the anterior end of the anterior fins, with large ova. Seminal vesicles located between the lateral fins, well marked, with a trunk and a large knob with two papillae. When fully mature, the vesicles touch almost the fins.
Hooks 5-9. Teeth in two rows, anterior 6-10 and posterior 12-20.
Maximum body length 13 mm, relative tail length 22-30%.
Distribution in the North Sea
S. serratodentata occasionally occurs in the S and N North Sea, entered from the respective adjacent NE Atlantic waters.
Epipelagic in temperate and warm Atlantic waters (occasionally in other oceans also).
[After Pierrot-Bults and Chidgey, 1988]