Structure and motility of the 9 + 0 flagellum of eel spermatozoa.

Scanning and electron microscopic study of the spermatozoon of the eel, Anguilla anguilla, has shown that the large oblong head is attached eccentrically by one end to the basal end of the true flagellum and contains a pseudoflagellum that splits into two groups of tubules as it passes around the nucleus. The 9+0 axoneme of the true flagellum lacks outer dynein arms and the radial spoke complex. The movement of Anguilla sperm is characterized by rapid forward progression that is the result of left-handed helicoidal waves propagated distally at a beat frequency at 21 degrees of about 95 Hz. Thus, these sperm flagella, although reduced in structure, propagate three dimensional rather than planar waves as in sea urchin sperm flagella, and beat at a frequency which so far as we know is the highest observed in eukaryotic flagella.