Temporal range: 220–0Ma
(Bosc, 1801) 
|The range of Triops cancriformis|
Due to habitat destruction, many populations have recently been lost across its European range, so, the species is considered endangered in the United Kingdom and in several European countries. In captivity they commonly grow up to 6 centimetres (2.4 in); in the wild they can achieve sizes of 11 cm (4.3 in).
In the UK, there are just two known populations: in a pool and adjacent area in the Caerlaverock Wetlands in Scotland, and a temporary pond in the New Forest. The species is legally protected under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended).
This species is considered to be one of the oldest living species on the planet at around 200 million years old. Fossils of this species from the Upper Triassic (Norian) period appear virtually unchanged compared to modern day members of the species.
Triops cancriformis has a very fast life cycle, and individuals become mature in about two weeks after hatching. Their populations can be gonochoric, hermaphroditic or androdioecious. The latter is a very rare reproductive mode in animals, in which populations are made of hermaphrodites, with a small proportion of males. Due to this lack of males, early researchers thought Triops were parthenogenetic. The presence of testicular lobes scattered amongst their ovaries confirmed they were in fact hermaphroditic. Fertilized females of hermaphrodites produce diapausing eggs or cysts, able to survive decades in the sediment of the ponds and lakes they inhabit. These eggs are resistant to drought and temperature extremes.
In 1801, Louis Augustin Guillaume Bosc made the first officially recognised species description of Triops cancriformis. He named this species Apus cancriformis. Other authors used the name Apus cancriformis over the years but often with the wrong original author of this name.
In 1909, Ludwig Keilhack used the correct name "Triops cancriformis (Bosc)" in a field identification key of the freshwater fauna of Germany. He took up the genus name proposed by Schrank and suggested that the genus name Apus be replaced with Triops Schrank. However, other authors disagreed with him and the controversy continued until the 1950s.
In 1955, Alan Longhurst provided the original author of T. cancriformis as "Triops cancriformis (Bosc, 1801)" with a full history of synonymy to support it. This was in a taxonomic review of the Notostraca that also supported using the genus name Triops instead of Apus. In 1958, the International Commission on Zoological Nomenclature (ICZN) recognised the name Triops cancriformis (Bosc, 1801–1802) (ICZN name no. 1476) as officially the oldest. They also recognised the genus name Triops Schrank instead of Apus. They followed Longhurst in these decisions.
- "Triops cancriformis". Integrated Taxonomic Information System.
- "Tadpole shrimp - Triops cancriformis". ARKive. Retrieved April 20, 2009.
- "Triops, the 300 million year-old living fossil". Planet Earth online. 22 December 2008. Retrieved 22 July 2009.
- Klaus-Peter Kelber - Triops
- Ole S. Møller, Jørgen Olesen & Jens T. Høeg (2003). "SEM studies on the early larval development of Triops cancriformis (Bosc) (Crustacea: Branchiopoda, Notostraca)" (PDF). Acta Zoologica 84 (4): 267–284. doi:10.1046/j.1463-6395.2003.00146.x.
- Alan R. Longhurst (1955). "A review of the Notostraca". Bulletin of the British Museum (Natural History) 3 (1): 1–57.