There is a surprising diversity of size, shape and number of sperm produced by different species.

Just as an example, sperm length varies by several orders of magnitude, and in general the larger the animal the smaller the sperm. For instance porcupine sperm is just 0.0003 cm long. Compare that with the sperm of fruit flies which is 6 cm in size — that’s some 20 times the length of the fly! This only works because the fruit fly’s sperm is like a ball of string which only unravels once inside the female’s reproductive tract (which is longer than the sperm!).
For more amazing facts about sperm see The Biggest Sperm Come In The Smallest Packages – And Other Odd Facts About Male Sex Cells.