Triops cancriformis

Triops cancriformis Temporal range: 220–0Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Branchiopoda
Order:	Notostraca
Family:	Triopsidae
Genus:	Triops
Species:	T. cancriformis
Binomial name
Triops cancriformis (Bosc, 1801) [1]
The range of Triops cancriformis

Triops cancriformis, or tadpole shrimp, 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.^[2] 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).^[2]

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.^[3] 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.^[4]

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.

Taxonomic history

In 1801, Louis Augustin Guillaume Bosc made the first officially recognised species description of Triops cancriformis.^[5] 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.^[5]

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.^[5]

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.^[6] 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.^[5]

References