Triops


Triops is a genus of small crustaceans in the order Notostraca. Some species are considered living fossils, with a fossil record that reaches back to the late Carboniferous,. The long lasting resting eggs of one species, Triops longicaudatus, are commonly sold in kits as a pet. In contact with fresh water the animals hatch. Most Triops have a life expectancy of up to 90 days, and can tolerate a pH range of 6–10. In nature they often inhabit temporary pools.

Relatives and fossil record

The genus Triops can be distinguished from the only other genus of Notostraca, Lepidurus, by the form of the telson, 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 attributable to this genus have been found in rocks of Carboniferous age, an estimated, and one extant species, Triops cancriformis, has hardly changed since the Jurassic period.
Triops can be found in Africa, Australia, Asia, South America, Europe, 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 the Greek s that lie close to each other and are nearly fused together. The compound eyes are generally sessile. In addition, there is a naupliar ocellus 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 Dreyauge, 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 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.
Although the taxonomy of the genus has not been reviewed since 1955, the following species are recognised:
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.

Human uses

The species 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 spadefoot frogs.
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. The red forms of T. longicaudatus and T. cancriformis are also fairly common among enthusiasts and have been the subject of numerous YouTube videos.
Captive Triops are frequently kept in aquariums 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.
They will also feed themselves by grazing on algae and detritus from the bottom and sides of the tank, and on small particles clinging to sponge filters or to Marimo moss balls which are often cultured alongside Triops.