This is a female crayfish brooding her recently hatched young in my classroom tank. Most malacostracans brood their eggs on their swimmerets (pleopods), until the the eggs hatch into a zoea or a nauplius, however freshwater crayfish have direct development, so they pass through those stages while still in the egg and hatch as crawl-away juveniles.
Male crayfish have specialized pleopods (gonopods) which are larger and stiffer to deliver sperm packets to the female's gonopore. They also tend to have narrower abdomens and the rest of their pleopods are smaller than the females. Reproduction must be timed closely with molting as the female's gonopore is an invagination of her exoskeleton. Mate too soon and the sperm packet will be lost with the old exoskeleton. The Y-organ at the base of the eyestalk is responsible for both gonad development and repression of molting.