Lepidurus apus, commonly known as a tadpole shrimp, is a notostracan in the family Triopsidae, one of a lineage of shrimp-like crustaceans that have had a similar form since the Triassic period and are considered living fossils.

However, a recent study suggests that resemblance to fossil notostracans is probably a result of the "highly conserved general morphology in this group and of homoplasy".

[citation needed] Lepidurus apus is perhaps the most cosmopolitan of all the Notostraca, occurring widely around the world including, but not limited to, New Zealand, Australia, Iran, [1] Israel, [4] France, Germany, Italy,[5] Denmark,[6] and Austria.

[7] Lepidurus apus is found predominantly in temporary freshwater ponds, 10–100 cm deep, filled during autumn and winter, and drying out over spring and summer.

[1] Wetlands and temporary ponds worldwide are increasingly being converted to grasslands for agriculture, so the total land area available for L. apus is gradually diminishing.

[7][9] L. apus is well-adapted to variations of climate and location, disperses easily, and has highly resilient eggs, so appears to be less sensitive to human pressures across its wide geographical range.

Lepidurus apus has an unusual life-cycle: it is able to produce microscopic cysts that can lie dormant for years at a time through extreme conditions, letting it survive in areas with vastly different climates such as Morocco and Denmark.

[1] Lepidurus apus is omnivorous, feeding on both plant matter, mostly floating detritus, and small aquatic invertebrates such as Branchinecta and Daphnia.

[2] Predators of Lepidurus include small wading birds such as sandpipers or stint, larger waterfowl like ducks and swans, and, in some ponds, fishes.

Nosema lepiduri is a microsporidian parasite found in water bodies less than 15 cm deep that internally parasitises Lepidurus with spores, in some cases killing the host.