showing a mix of the two. The frequency of males in populations is therefore highly variable. In sexual populations, the sperm leave the male's body through simple pores, there being no penis. The eggs are released by the female and then held in the cup-like brood pouch. The eggs are retained by the female only for a short time before being laid, and the larvae develop directly, without passing through a metamorphosis. Ecology and distribution Notostracans are omnivorous, eating small animals such as fishes and fairy shrimp. They are found worldwide in freshwater, brackish water, or saline pools, as well as in shallow lakes, peat bogs, and moorland. The species Triops longicaudatus is considered an agricultural pest in California rice paddies, because it prevents light from reaching the rice seedlings by stirring up sediment. Evolution and fossil record The fossil record of Notostraca is extensive, occurring in a wide range of geological deposits. The oldest known notostracan is the species Strudops goldenbergi from the Late Devonian (Famennian ~ 365 million years ago) of Belgium. The lack of major morphological change since has led to Notostraca being described as living fossils. Kazacharthra, a group known only from Triassic and Jurassic fossils from Kazakhstan and Western China, are closely related to notostracans, and may belong within the order Notostraca, or alternatively are placed as their sister group within the clade Calmanostraca. The "central autapomorphy" of the Notostraca is the abandonment of filter feeding in open water, and the development of a benthic lifestyle in muddy waters, taking up food from particles of sediment and preying on small animals. A number of other characteristics are correlated with this change, including the increased size of the animal compared to its relatives, and the loss of the ability to hinge the carapace; although a central keel marks the former separation into two valves, the adductor muscle is missing. Notostracans retain the plesiomorphic condition of having two separate compound eyes, which abut, but have not become united, as seen in other groups of Branchiopoda. Taxonomy The extant members of order Notostraca composed a single family, Triopsidae, with only two genera, Triops and Lepidurus. The problematic Middle Ordovician fossil Douglasocaris has been erected and placed in its own family Douglasocaridae by Caster & Brooks 1956, and may be ancestral to Notostraca. The phenotypic plasticity shown by notostracan species make identification to the species level difficult. Many putative