Someone was looking for a sperm STL, so I made a sperm STL! 

Flat bottom, print-in-place quick print. Scales up easily, scaling down might lose some of the tail.

Split the model into Objects to separate the two sperm. Flip/mirror them to get variations!

Standard settings should work, maybe try a thinner layer height than usual for tail details. 0.16 instead of .2 for example.