Triops, or tadpole and shield shrimp as they are sometimes called, are a small group of crustaceans that are found in temporary bodies of fresh to brackish water. Sometimes sold in Sea-Monkey like kits, they are billed as "living fossils". The moniker 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. 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 extant species.

Triops cancriformis

The branchiopods are a primitive order of crustaceans. Lacking true gills, they breathe with leaf-like extensions on their legs. Scientists, being so original when it comes to these things, named them for this; branchiopod means "lung or gill foot". The alternative name for the branchiopods, phyllopods, is equally original, it means "leaf foot". There are four extant orders of branchiopods: Anostroca, Cladocera, Conchostroca, and Notostraca. The anostracans contain the brine shrimp and numerous species of fairy shrimp. The cladocerans are composed of the daphnia species ("water fleas"). The conchostractans contain the lesser known clam shrimp. Finally, the notostracans are composed of various species of tadpole shrimp, often known as triops. Generally, biologists group the anostrocans, conchostrocans, and notostrocans together as the (also originally named) "large branchiopods".

The notostracrans contain only a single family, triopsidae, and two genera, Lepidurus and Triops. All triops share a common body plan that looks something like a cross between a horseshoe crab and the extinct trilobites. Commonly billed as "living fossils", their appearance certainly fits this description. Species from both genera look very similar except for the key distinguishing characteristic of Lepidurus species: in between the two tail spines, Lepidurus species have a distinct supra anal plate. In Triops species this plate is either absent or extremely reduced. Sizes vary from species to species, but none are very large. T. cancriformis holds the size record with one wild caught specimen reported to measure 11 cm (almost 4.5 inches!).

Triops live in temporary water pools (also known as vernal, astatic, or ephemeral pools) that generally occur during seasonal rains or flooding. As a rule of thumb, Triops species tend to be found in areas where warmer, shorter lasting pools are common, and Lepidurus species are found where cooler, longer lasting pools are the rule. Not only might a given pool only last a few weeks before completely drying out, it may be years, or even decades, before the water comes again if rainfall is erratic. How a creature that breathes with primitive gills is able to survive these conditions is why they have lasted through the aeons when so many other species have not.

last updated October 28, 2000