When it comes to sex, there are no fixed rules in the animal world. The barnacle is the most well-endowed of all males, but it is also a female.
Some species start out as females and later become males.
Palolo worms indulge in mass orgies on one special night of the year. The process of fertilization can be fraught with great difficulties. Timing may have to be precise. Those involved may be temporarily defenseless. It can risk injury or cause certain death.