What are triops? Are they insects? fish? No, triops are a small crustacean, sometimes called the tadpole shrimp. They are considered to be living fossils, some species having remained unchanged for over 180 million years. The reason that they make good pets is that their eggs can remain viable even when completely dried out. It’s an evolutionary strategy that enables them to survive in areas when temporary pools exist, they feed and breed when the rains form pools and puddles and then survive as eggs when the pools dry out.
The following snippet, from the estimable Wikipedia gives an idea of the evolutionary background of these fascinating creatures:
The genus Triops can be distinguished from the only other genus of Notostraca, Lepidurus, by the form of the telson, which bears a pair of long, thin caudal extensions in Triops, while Lepidurus bears a central platelike process. Triops are sometimes called “living fossils”. Fossils attributable to this genus have been found in rocks of Carboniferous age, 300 million years ago, and one extant species, Triops cancriformis, has hardly changed since the Jurassic period (approximately 180 million years ago). Life cycle
Most species reproduce sexually, but some populations are dominated by hermaphrodites which produce internally fertilised eggs. Reproduction in T. cancriformis varies with latitude, with sexual reproduction dominating in the south of its range, and parthenogenesis dominating in the north. Triops eggs enter a state of extended diapause when dry, and will tolerate temperatures of up to 98 °C (208 °F) for 16 hours, whereas the adult cannot survive temperatures above 34°C (93°F) for 24 hours or 40 °C (104°F) for 2 hours. The diapause also prevents the eggs from hatching too soon after rain; the pool must fill with enough water for the dormancy to be broken.