out of the anterior opening by peristalsis. The nervous system consists of two nerve cords which run the length of the body, with two ganglia and two transverse commissures in most of the body segments. Gas exchange is thought to take place through the entire body surface, but especially that of the phyllopodia and their associated gills, which may also be responsible for osmotic regulation. Two coiled glands at the bases of the maxillae are used to excrete nitrogenous waste, typically in the form of urea. Most of the animal's nitrogenous waste is, however, in the form of ammonia, which probably diffuses into the environment through the phyllopodia and gills. Ecology and behaviour Anostracans inhabit inland waters ranging from hypersaline lakes to lakes that are almost devoid of dissolved substances; they are "the most archetypal crustaceans" in ephemeral waters. The relatively large size of fairy shrimp, together with their slow means of locomotion, makes them an easy target for predatory fish and waterfowl. This has led to their distribution being restricted to environments with fewer predators, such as vernal pools, salt lakes and lakes at high altitudes or latitudes. The southernmost recorded fairy shrimp is Branchinecta gaini from the Antarctic Peninsula, while the altitude record is held by B. brushi, which lives at in the Chilean Andes. Other genera, such as Streptocephalus, occur in deserts throughout the world. Anostracans swim gracefully by movements of their phyllopodia (thoracic appendages) in a metachronal rhythm. When swimming, the animal's ventral side is normally uppermost (often described as swimming "upside-down"). They filter food indiscriminately from the water as they swim, but also scrape algae and other organic materials from solid surfaces, for which they turn to have their ventral side against the food surface. Another important aspect of the fairy shrimp’s life cycle is their universal ability to enter diapause, a state of biological dormancy where growth and metabolism are arrested, as an egg (or cyst). This trait assists in both species' dispersal and in overcoming adverse environmental conditions. Once dormant, these cysts can withstand conditions as harsh and diverse as droughts, frosts, hypersalinity, complete desiccation, exposure to UV radiation and the vacuum of space. It is also the only way for the fairy shrimps to colonize new habitats—facilitated by a variety of conditions including wind, predators, currents—as the soft-bodied adults are unable to leave the freshwater system. Once in diapause, these cysts can