Table 1.

The defined morphology of sperm tail

Term	Standards according to the 5th edition of the WHO standards (2010)
No tail	Isolated head, no tail observed
Short tail	A tail length (mid-piece plus principal piece) no more than five  times the major axis length of the head
Bent/  misaligned tail	May include neck anomalies, misalignment of the head major  axis and midpiece axis or an acute angle (≤120°) between the  head major axis and midpiece axis or an acute angle (≤120°)  between the midpiece and the principal piece axes
Coiled tail	Completely or partially coiled tail, with the coil close to or  around the head (flat coiling or coiling at the extremity of the  tail reminiscent of hypo-osmotic coiling aspects should not be  included in this category)
Irregularly  shaped tail	Irregular width of the midpiece or changing calibre of the principle  piece; or the principle piece is not thinner than the midpiece