Triops, sometimes called tadpole, dinosaur or shield shrimp, are a small group of crustaceans that are in the Branchiopoda group that are found in temporary bodies of fresh or brackish water. Sometimes they are sold in 'Sea-Monkey' like kits in toy shops, they are often billed as "living fossils". This name is well earned, this truly ancient group has survived virtually unchanged for roughly three hundred million years. The oldest triops fossils date back to the Carboniferous Paleozoic and the world's oldest known living animal species is a triops, Triops cancriformis.
T. cancriformis fossils date back 200 million years ago to the Triassic age. There were triops swimming around in pools of water when the first dinosaurs walked the Earth, and 65 million years after the last dinosaur took a breath, the triops are still here!
In the time that the triops have been here, the Earth has undergone countless changes. "The land has gone from a single super continent, Pangea, to the seven continents of today. The climates have cycled hot and cold and back again many, many times. Almost every animal species alive today has evolved since the triops appeared on the scene. Thousands of more species evolved within that time, thrived for a bit, and were driven exinct for one reason or another.
The triops have been there through it all.They are, in every sense of the word, biological marvels of survival and niche adaptation. They have done more than just survive, though. Today, triops are found on every continent except Anarctica and there are at least 15 known species.
The most common species of triops you can buy over the counter is the american Triops longicaudatus. This is a more golden coloured animal and usually grows slightly smaller than Triops cancriformis and requires a touch warmer water temperature to live in.
Triops cancriformis has been seen in the wild up to 11cm (4.5") in length (not including the tail). But it's more usual to see this species in a tank grow up to 8cm (3") in length. The average Triops longicaudatus will grow up to 6cm (2.5") in a tank.