Females in such cases may be endowed with effective mechanisms to keep off males from copulatory attempts. A few hours or days after copulation eggsacks are formed by the female. Most species produce paired eggsacks . These sacks are carried outside the body under the abdomen and consist of eggs embedded into a mass of secretions. Depending on size and life style a few to several dozen eggs develop inside their protective cover.
Some parasites produce several thousand eggs.
The eggs are probably still nourished by the females. After a few days the larvae hatch and the eggsack is cast off. Usually they pass six naupliar stages, which are separated by a moult. The first stages have only three pairs of appendages that are responsible for locomotion and feeding. The older nauplii already show buds of further mouth appendages and swimming legs.