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Triops cancriformis, or tadpole shrimp (not to be confused with horseshoe crabs), is a species of tadpole shrimp found in Europe, the Middle East and Japan.

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); however, 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 period appear virtually unchanged compared to modern day members of the species.

Life cycle[]

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.

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