A hatching cyst of a brine shrimp.

The picture shows a group of cysts (green) of the brine shrimp, Artemia sp. The cyst above center right has hatched to produce a nauplius larva, with a smooth The cyst above right has hatched to produce a nauplius larva, with a smooth outer surface, (here pink). Artemia is a primitive arthropod; its common name arises from its preferred habitat, which is water of very high salinity, often in the range 60-80% salt. Cysts are produced by females under conditions of low oxygen saturation or very high salt levels (150%). The cysts are capable of surviving in an inert metabolic state for several years in the absence of oxygen, and at temperatures below freezing, including Brought into favourable conditions, the cysts produce nauplii within hours, and are traded as a convenient source of food for fish farms. Artemia nauplii have been used as a model species for toxicity testing of environmental pollutants. SCIENCE PHOTO LIBRARY