Except for some members of the genus Artemia, fairy shrimp are bisexual and oviparous, usually with marked structural differences between the sexes. In males, the second antenna is modified into a remarkably complex clasping organ that is used to hold the female during copulation. In addition to the clasping organ, male anostracans have two penes. Copulation may take place so rapidly as to be hardly visible to the unaided eye, as in most streptocephalids; or last for many hours as the couple swims around in tandem formation, as in Artemia.
Following copulation and internal fertilization, the eggs are deposited in an external brood pouch of variable shape.
Each batch, or clutch, may contain several hundred eggs, and a female may produce up to forty clutches in her lifetime; thus total fertility may reach 4,000 eggs per female. The eggs are usually shed freely into the water. They may either sink to the bottom, as is usually the case in freshwater species, or float on the surface, to be deposited eventually along the lake shore.
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