Triops, from Ancient Greek (), meaning "three", and (), 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. 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. but subsequent analysis consider it as a separate genus. 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.), 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. 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.

thumb|350px|Upper and underside Triops. 1 eyes, 2 antennae, 3 tail, 4 torso, 5 antenne, 6 1st torso appendix, 7 legs with gill, 8 middelline, 9 tail, 10 anus

Franz von Paula Schrank was the first author to use the genus name Triops, 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'.

  • Triops australiensis <small>(Spencer & Hall, 1895)</small>
  • Triops baeticus <small>Korn, 2010</small>
  • Triops cancriformis <small>(Bosc, 1801)</small>
  • Triops emeritensis <small>Korn & Pérez-Bote, 2010</small>
  • Triops gadensis <small>Korn & García-de-Lomas, 2010</small>
  • Triops granarius <small>(Lucas, 1864)</small>
  • Triops longicaudatus <small>(LeConte, 1846)</small>
  • Triops mauritanicus <small>Ghigi, 1921</small>
  • Triops newberryi <small>Thomas, 1921</small>
  • Triops vicentinus <small>Korn, Machado, Cristo & Cancela da Fonseca, 2010</small>

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

thumb|Triops cancriformis "Beni-Kabuto Ebi Albino" showing translucent carapace. As the animal grows the carapace will become more opaque but will never take on the color pattern normally associated with T. cancriformis.

thumb|Captive Triops cancriformis (left) and Triops longicaudatus (right) feeding on carrot.

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. Due to their broad dietary range, they can be fed various items, including lunch meat, crackers and potatoes.

In the US state of 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

  • 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