Triops

''Triops'', from Ancient Greek τρία (''tría''), meaning "three", and ὄψ (''óps''), meaning "face" or "eye", is a genus of small crustaceans in the order Notostraca (tadpole shrimp). The long-lasting resting eggs of several species of ''Triops'' are commonly sold in kits as pets. The animals hatch upon contact with fresh water. Most adult-stage ''Triops'' have a life expectancy of up to 90 days and can tolerate a pH range of 6 to 10. In nature, they often inhabit temporary pools.

Relatives and fossil record

The genus ''Triops'' can be distinguished from the only other living genus of Notostraca, ''Lepidurus'', by the form of the telson (the end of its 'tail'), which bears only a pair of long, thin caudal extensions in ''Triops'', while ''Lepidurus'' also bears a central platelike process. Only 24 hours after hatching they already resemble miniature versions of the adult form.

''Triops'' are sometimes called "living fossils", since fossils that have been attributed to this genus have been found in rocks hundreds of millions of years old. Molecular clock estimates suggest that ''Triops'' split from ''Lepidurus'' during the Triassic or Jurassic, between 152.3–233.5 million years ago. The earliest diverging lineages of living ''Triops'' are found in areas that are part of the former supercontinent Gondwana, suggesting ''Triops'' originated in Gondwana. However, the earliest known definitive fossil attributed to ''Triops'' is known from the Early Miocene of Japan, and careful analysis of the pre-Cenozoic fossils suggest that they do not belong to ''Triops'', with some not even belonging to notostracans.

The Upper Carboniferous genus ''Lynceites'' was once thought to represent ''Triops'', but subsequent analysis consider it as a separate genus. Fossils from the Lower Triassic of France and Upper Triassic of Germany have been previously attributed to '' Triops cancriformis'', with some even described as specimens of the subspecies ''T. c. minor'', but later research reassigned all of these Triassic specimens to different extinct taxa of uncertain taxonomic family: the notostracan ''Apudites antiquus'' and the diplostracans ''Olesenocaris galli'' and ''Grauvogelocaris alsatica''. The putative Lower Permian subspecies of ''Triops cancriformis'' from France has also been redescribed as a separate notostracan taxon, ''Heidiops permiensis''. Two putative fossil species of ''Triops'', ''T. hanshanensis'' and ''T. bashuensis'', known from the Middle Jurassic of China likely belong to separate genera with features unknown in any extant or extinct species of notostracans.

''Triops'' can be found in Africa, Australia, Asia, South America, Europe (including Great Britain), and in some parts of North America where the climate is right. Some eggs stay unhatched from the previous group and hatch when rain soaks the area. ''Triops'' are often found in vernal pools.

Life cycle

Most species reproduce sexually, but some populations are dominated by hermaphrodites which produce internally fertilised eggs. Reproduction in ''T. cancriformis'' varies with latitude, with sexual reproduction dominating in the south of its range, and parthenogenesis dominating in the north.

''Triops'' eggs enter a state of extended diapause when dry, and will tolerate temperatures of up to for 16 hours, whereas the adult cannot survive temperatures above for 24 hours or for 2 hours. The diapause also prevents the eggs from hatching too soon after rain; the pool must fill with enough water for the dormancy to be broken.

Taxonomy

The name ''Triops'' comes from Ancient Greek τρία (''tría''), meaning "three", and ὄψ (''óps''), meaning "face" or "eye". The head of ''T. longicaudatus'' bears a pair of dorsal compound eyes that lie close to each other and are nearly fused together. The compound eyes are generally sessile (not stalked). In addition, there is a naupliar ocellus (the "third eye") between them. The compound eyes are on the surface of the head, but the ocellus is deep within the head. All the eyes, however, are easily visible through the shell covering of the head.

Franz von Paula Schrank was the first author to use the genus name ''Triops'', coining it in his 1803 work on the fauna of Bavaria. Their German name was ', which means 'three-eye'. He collected and described specimens from the same locality in Regensburg from which Schäffer, another naturalist who had studied the Notostraca, obtained his specimens in the 1750s. However, other authors, starting with Louis Augustin Guillaume Bosc, had adopted the genus name ''Apus'' for the organisms Schrank had named ''Triops''

Ludwig Keilhack used the genus name ''Triops'' in his 1909 field identification key of the freshwater fauna of Germany. He suggested that the genus name ''Apus'' be replaced by ''Triops'' Schrank since an avian genus had already been described by Giovanni Antonio Scopoli under the name ''Apus''. However, Robert Gurney preferred the name ''Apus'' Schäffer. He suggested that the name '…''Triops'' Schrank, may be returned to the obscurity from which it was unearthed'. This controversy continued and was not resolved until the 1950s.

In his 1955 taxonomic review of the Notostraca, Alan R. Longhurst supported Keilhack's genus name ''Triops'' over ''Apus''. Longhurst provided historical evidence to support this position. The International Commission on Zoological Nomenclature (ICZN) followed Longhurst in their 1958 ruling on the usage and origin of the genus names ''Triops'' and ''Apus''. They rejected the genus name ''Apus'' and instead recognized the genus name ''Triops'' Schrank, 1803 (ICZN name no. 1246).

Although the taxonomy of the genus has not been reviewed since 1955, the following species are recognised:
* '' Triops australiensis'' (Spencer & Hall, 1895)
* '' Triops baeticus'' Korn, 2010
* '' Triops cancriformis'' (Bosc, 1801)
* '' Triops emeritensis'' Korn & Pérez-Bote, 2010
* '' Triops gadensis'' Korn & García-de-Lomas, 2010
* '' Triops granarius'' (Lucas, 1864)
* ''Triops longicaudatus'' (LeConte, 1846)
* '' Triops mauritanicus'' Ghigi, 1921
* '' Triops newberryi'' Thomas, 1921
* '' Triops vicentinus'' Korn, Machado, Cristo & Cancela da Fonseca, 2010

''T. mauritanicus'' was considered a subspecies of ''T. cancriformis'' by Longhurst in 1955, but was given full species status again by Korn ''et al.'' in 2006.

Note that for several of these species there are different varieties, some of which have recently been suggested as subspecies and even separate species. ''T. longicaudatus'', for example, may actually be several species lumped together, and '' T. cancriformis'' is generally recognized as having three subspecies: ''T. cancriformis cancriformis'',
''T. c. mauretanicus'', and ''T. c. simplex''. Also, the albino form has the special name of ''T. cancriformis'' var. ''Beni-Kabuto Ebi''.

Relationship with humans

''T. longicaudatus'' is considered a human ally against the West Nile virus, as the individuals consume '' Culex'' mosquito larvae. They also are used as a biological pest control in Japan, eating weeds in rice paddies. The Beni-Kabuto Ebi Albino variant of ''T. cancriformis'' is particularly valued for this purpose. In Wyoming, the presence of ''T. longicaudatus'' usually indicates a good chance of the hatching of American spadefoot toads.

Dried eggs of ''T. longicaudatus'' are sold in kits to be raised as aquarium pets, sold under the name of "aquasaurs", "trigons" or "triops". Among enthusiasts, ''T. cancriformis'' is also common. Other species often encountered in captivity include '' T. australiensis'', '' T. newberryi'' and '' T. granarius''.

Captive ''Triops'' are frequently kept in aquaria and fed a diet consisting mainly of carrots, shrimp pellets and dried shrimp. Often they are also given living shrimp and ''Daphnia'' as live prey. Because they can feed on just about anything they are also fed lunch meat, crackers, potatoes etc.

In California, ''T. longicaudatus'' has emerged as a significant pest of rice cultivation, due to its digging behaviour uprooting young rice seedlings.

See also

* Notostraca
* Lepidurus
* Xiphosura
* Synziphosurina
* Trilobite

References

External links

Discussing Triops (r/Triops)
��A Reddit community devoted to their care and ecology.

Mytriops.com
��Website with useful information about ''Triops'' and keeping ''Triops'' as pets.

Triops
��YouTube video on raising ''Triops''

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Notostraca
Branchiopoda genera
Extant Miocene first appearances
Taxa named by Franz von Paula Schrank
Animals bred for albinism on a large scale