Notostraca 1102900 217855976 2008-06-08T00:42:27Z Epbr123 1395162 Reverted edits by [[Special:Contributions/69.37.125.179|69.37.125.179]] to last version by ClueBot (using [[WP:HG|Huggle]]) {{Taxobox | name = Notostraca | image = Triops_longicaudatus.jpg | image_width = 250px | image_caption = ''[[Triops longicaudatus]]'' | regnum = [[Animal]]ia | phylum = [[Arthropod]]a | subphylum = [[Crustacean|Crustacea]] | classis = [[Branchiopoda]] | ordo = '''Notostraca''' | ordo_authority = [[Georg Sars|G. O. Sars]], 1867 | familia = '''Triopsidae''' | familia_authority = [[Keilhack]], 1909 | subdivision_ranks = [[Genus|Genera]] | subdivision = *''[[Lepidurus]]'' *'''''Triops''''' }} Members of the [[Order (biology)|order]] '''Notostraca''' (colloquially referred to as '''notostracans''', called '''''Triops''''', '''tadpole shrimp''' or '''shield shrimp''') are small [[crustacean]]s in the [[Class (biology)|class]] [[Branchiopoda]]. Triops have two internal [[compound eye]]s and one [[Nauplius (larva)|naupliar]] eye in-between, a flattened [[carapace]] covering its head and [[arthropod leg|leg]]-bearing [[body segment|segments of the body]]. The order contains a single [[family (biology)|family]], with only two [[Extant taxon|extant]] [[genus|genera]]. Their external morphology has apparently not changed since the [[Triassic]] appearance of ''Triops cancriformis'' around 220 million years ago. ''Triops cancriformis'' may therefore be the "oldest living animal species on earth."&nbsp;<ref>Kelber, K.-P. (1999). ''Triops cancriformis.'' (Crustacea, Notostraca): Ein bemerkenswertes Fossil aus der Trias Mitteleuropas. — ''In'': Hauschke, N. & Wilde, V. (''eds.''): Trias - Eine ganz andere Welt, '''III.16''': ''383-394''. Verl. Dr. F. Pfeil, Munich.</ref> The members of the extinct order [[Kazacharthra]] are closely related, having been descended from notostracans. == Characteristics == Although notostracans are related to [[fairy shrimp]]s, they differ greatly in structure. The flat oval shield covers the crustacean's head and the front part of the thorax. Near the front edge of the shield, on its surface, is a small lump that bears two dark, stalkless, compound eyes. In between them is an unpaired [[Nauplius (larva)|naupliar]] eye, and behind the three eyes is an unusual ''four-celled organ''. The function of this organ is uncertain. It is thought to be an internal [[secretion]] organ. The hind edge of the shield is a semicircular dent that leaves the hind portion of the [[thorax]] exposed. The [[abdomen]] ends with a [[telson]] that bears two long segmented [[uropod]]s, known as furcae. By looking at a tadpole shrimp from the [[ventral]] side one can clearly see the structure of its segments and limbs. In front, the [[carapace]] curves down to the ventral side, where it attaches to a large labrum (upper lip) that is almost square in shape. The first and second pair of antennae is extremely reduced in size, while the [[Mandible (arthropod)|mandibles]] are quite large, with many toothlike projections. The mouth is located in between the mandibles, behind the labrum. Behind the mandibles are one or two pairs of flat jaws (maxillae). The next 10 thoracic segments each bear a pair of legs. As in fairy shrimps, the legs have 6 lobes on the inner side that push the food towards the mouth; on the outer side is one large swimming lobe and one breathing lobe, modified into a gill (fairy shrimps have two breathing lobes on each leg). Detailed muscle studies conclude that the legs of tadpole shrimps and fairy shrimps have no [[phylogenetic]] relationship, apparently having evolved independently, albeit with similar functions. The first and, less obviously, second pair of a tadpole shrimp's legs differs from other legs by the four inner lobes, which are modified into elongated, segmented, [[flagellum]]-like structures that project outside from the edge of the carapace. They act as sensory organs and even resemble externally the flagella of the antennae of other [[crustacean]]s. This modification of the inner lobes of the front thoracic legs is unquestionably associated with the reduction of the tadpole shrimp antennae. In females, the eleventh pair of limbs is quite unusual in structure: the large outer lobe, which is used for swimming in other limbs, is modified into a round egg capsule, where the eggs are carried. In males, the eleventh pair of legs does not differ from the other legs. There is another surprising phenomenon in the structure of tadpole shrimps. Every thoracic segment, from the thirteenth one on, bears not one, but 4 to 6 pairs of legs. Therefore, the number of pairs of the crustacean's legs often reaches as many as 70. No other crustacean has as many legs as tadpole shrimps. The legs gradually become smaller from front to back, while the posterior-most segments bear no legs at all. An obvious difference between tadpole shrimp and fairy shrimp legs is that the former possess several spikes at the base of each front leg, pointing inward. Tadpole shrimps use the spikes to grab large food particles and pass it from one leg to another forward, to the mouth. While fairy shrimps filter small food particles suspended in the water, notostracans apparently cannot do this. Their hind limbs mostly aid in respiration. It is quite noticeable during the crustacean's brief stops that its rear limbs continue moving, while the front ones keep still. As a tadpole shrimp swims, its legs bend and straighten in a wavelike motion. The Swedish zoologist Lundblad once droppered some water mixed with [[carmine]] near a tadpole shrimp's hind legs. He observed as the water moved slowly forward through the groove between the crustacean's hind legs. However, as soon as the water reached the tenth pair of legs, it streamed forward steadily, which showed how important the front limbs are in the process of bringing food up to the mouth. When a tadpole shrimp swims, its eyesight plays an important role. Lighting up the bottom of an [[aquarium]] in a dark room makes the crustacean roll over, ventral side up: the [[dorsal]]ly positioned eyes can then sense the light. Even when the crustacean's eyes are lacquered and it sits on the bottom of the aquarium ventral side down, the experiment brings the same result. Apparently, the tadpole shrimp reacts to the light because the naupliar eye compartment continues down as a connective passage and ends at the ventral side, in front of the upper lip, as a pigmentless "window". Thus, tadpole shrimps can sense light from above and below, simultaneously. Notostracans do not use their eyes to find food. They use a special chemical sense, centred in the flagellum-like inner outgrowths on the first pair of legs. A tadpole shrimp can easily find an [[earthworm]] in an aquarium and eat it. However, studies show that when [[quinine]] is added to the worm, the crustacean feels the serving with its flagella and refuses to eat the distasteful food. == Life cycle == In the northern hemisphere, tadpole shrimps mainly hatch from unfertilized eggs. The populations of the [[North America]]n and [[Eurasia]]n puddles and pools are made up almost exclusively of females. There is often less than 1 male per 100 females, and some pools contain no males at all. As one travels north to south, however, the males increase in numbers; in the tropics they may even outnumber the females. Due to the rareness of the males, mating tadpole shrimps have only been observed twice. The male attached himself to the female's carapace and bent his body so that a good deal of it was under the female. Next, he grabbed the female's eleventh pair of legs with his eleventh pair of legs. Both fertilized and unfertilized eggs are stored in the female's egg compartment on the 11th pair of legs. She keeps the eggs there for a short period of time and releases them to the bottom of the pool. What is interesting about them is that no differences in the structure, hatching rate or development of the two kinds of eggs can be observed. [[Image:Triops eggs.JPG|thumb|Batch of Notostracans eggs mixed with soil]] These tiny eggs are equipped with a strong, thick shell. They can withstand freezing, drought and can hatch as long as 9 years after the release. The eggs can stand temperatures of up to 80°C, or pass through a [[frog]]'s intestine without any harm at all. They are easily carried by the wind, even for very long distances. Due to these qualities of eggs, tadpole shrimps are common around the world. Their sudden appearance in some small pool is explained by their diapaused eggs ending up in the pool, and not adult crustaceans falling from the sky, as certain local inhabitants think. If the egg arrives in a pool with suitable conditions, the larva hatches a year later. In the common species ''Triops cancriformis'' this larva is a typical [[nauplius (larva)|nauplius]], with three pairs of limbs and no traces of segmentation. In other tadpole shrimp species the larva hatches at a later stage - the [[metanauplius]], characterized by a segmented hind part of the body. In order to reach sexual maturity, ''Triops cancriformis'' must [[Ecdysis|moult]] about 40 times. These moults follow one another very quickly and at summer temperature, the development from a nauplius to an adult crustacean takes only about two weeks. The spring tadpole shrimp (''Lepidurus apus'') reaches a length of 12 mm after 17 moults, while the [[sexual dimorphism]] appears after the 14th moult. The [[maximum life span]]s in the lab agree with data from field observations on ''Triops'' survival. In the lab, ''T. longicaudatus'' has a maximum lifespan of about 50 days and ''T. cancriformis'' a maximum lifespan of about 90 days, with some individuals beginning to die off as soon as two weeks after [[hatching]]. Secondarily, some may suffer premature deaths from [[ecdysis|moulting]] complications or other reasons. ==Ecology== Tadpole shrimps usually live near the ground of astatic pools, where they move with their [[ventral]] side down. However, [[hypoxia (environmental)|lack of oxygen]] can force them to swim upside-down with their gill-like legs close under the surface of the water. Notostraca are [[omnivore|omnivorous]]; they dig around in the mud using the frontal part of their shield, looking not only for [[plankton]] but also for larger prey such as [[worm]]s, [[chironomid]] [[larva]]e, small, dying or weak [[tadpole]]s, and even each other. [[Fairy shrimp|Anostraca]]ns, often associated with notostracans, can also be a considerable part of their prey (especially when weak or dying). Notostracans sometimes even [[cannibalism|cannibalise]] freshly [[ecdysis|moulted]], or even smaller members of the same species. In [[Northern Europe|northern]] and [[central Europe]], with few exceptions, all tadpole shrimps are female, whereas the sexes in [[Southern Europe|southern]] and [[western Europe]] as well as in northern [[Africa]] are nearly equal in number. These "females" possess hermaphroditic glands, but instead of selfing, [[parthenogenesis]] takes place. ''Triops'' survives in temporary pools all over the world, and are correspondingly short-lived. These ponds usually dry up during certain times of the year when there is no rainfall. Although the adult ''Triops'' die during these droughts, their embryos remain in a state of [[diapause]] (suspended animation) and can survive for several years until the next rains fill up the pools again, allowing them to hatch. ''Triops'' are often the [[Apex predator|top predators]] in [[vernal pool]]s, as they will eat anything smaller than themselves. They also are an important food source for visiting birds. In some areas, certain species of ''Triops'' are considered pests, as they damage young [[rice|rice plants]] by uprooting them while searching for food. ==Distribution== Notostracans can be found on every continent except [[Antarctica]]. In [[Austria]], two notostracan species (one spring species and one summer species) are documented: ''Lepidurus apus'' and ''Triops cancriformis''. In [[Americas|the Americas]], several species have been identified, including ''Triops longicaudatus'' and ''Triops newberryi''. In [[Australia]], ''Triops australiensis'' is found. Other common types are ''Triops numidicus'' from Africa, although it has been said that some papers refer to this as an outdated name for ''Triops granarius'', which is from South Africa, China, Japan and Italy&nbsp;<ref>{{cite web |url=http://filebox.vt.edu/users/channum/triops_species2.htm |title=Species descriptions |date=2001 |accessdate=2006-07-31}}</ref>. ''Triops cancriformis'' is also found in elsewhere in Europe, for example in Britain where it is endangered, occurring only in pools in two localities, one being in [[England]] at [[New Forest]] the other in [[Scotland]] at [http://www.wwt.org.uk/visit/caerlaverock/ Wildfowl & Wetlands Trust Caerlaverlock], which is near [[Dumfries]]. == Etymology of the word "Triops"== "Triops" is a loanword from [[Greek language|Greek]], meaning "three eyes." Notostracans, indeed, have three eyes, in that, unlike in the related [[Fairy shrimp]]s, the naupliar ocellus (the eye of the nauplius) is retained in the adult form, even as the two [[compound eye]]s develop. The two compound eyes look out for food and predators, but they can only see clearly for a short distance. The naupliar ocellus senses light, acting as an internal "compass".(In their natural habitat, the sun shines from above, therefore the animals believe that light is where "up" is.). Both the singular and plural is ''Triops''.&nbsp;<ref>[http://mytriops.com/ MyTriops Home Page<!-- Bot generated title -->]</ref> == Pop Culture References == [[They Might Be Giants]] have a song entitled "Triops Has Three Eyes" on their children's album "Here Come the 123s." It was included in their weekly kids podcast on 4/18/2008.[http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?i=25073452&id=268647482] ==Diversity== [[Image:Triops australiensis.jpg|300px|thumb|''Triops australiensis'']] [[Image:Triops cancriformis2.jpg|300px|thumb|''Triops cancriformis'']] [[Image:Triops longicaudatus 3.jpg|300px|thumb|right|''Triops longicaudatus'']] In spite of the wide distribution in still freshwater pools from [[subarctic]] ponds to hot tropical puddles, the order Notostraca comprises a paradoxically small number of species. Modern zoologists, taking the variety of all crustaceans into account, recognize only 16 species of tadpole shrimps worldwide - 6 species of the genus ''Triops'' and 10 species of the genus ''Lepidurus''. Some of them, such as ''Triops cancriformis'' and ''Lepidurus apus'', generally occur worldwide, while others, such as ''Lepidurus arcticus'', are confined to [[Arctic]] pools. There are certain exclusively [[Africa]]n species and exclusively [[Australia]]n species. ===Classification=== Genus ''[[Lepidurus]]'' <small>[[William Elford Leach|Leach]], 1819</small> *''[[Lepidurus apus]]'' <small>([[Carolus Linnaeus|Linnaeus]], 1758)</small> *''[[Lepidurus arcticus]]'' <small>([[Peter Simon Pallas|Pallas]], 1776)</small> *''[[Lepidurus batesoni]]'' <small>[[Lonhorst]], 1955</small> *''[[Lepidurus bilobatus]]'' <small>[[Packard]], 1883</small> *''[[Lepidurus couesii]]'' <small>[[Packard]], 1875</small> *''[[Lepidurus cryptus]]'' <small>[[Rogers (surname)|Rogers]], 2001</small> *''[[Lepidurus lemmoni]]'' <small>[[Holmes]], 1894</small> *''[[Lepidurus lynchi]]'' *''[[Lepidurus mongolicus]]'' <small>[[Vekhoff]], 1992</small> *''[[Lepidurus packardi]]'' Genus ''Triops'' <small>[[Franz Paula von Schrank|Schrank]], 1803</small> *''[[Triops australiensis]]'' <small>(Spencer & Hall, 1895)</small> *''Triops cancriformis'' <small>([[Louis Augustin Guillaume Bosc|Bosc]], 1801)</small> *''[[Triops granarius]]'' <small>[[Lucas]], 1864</small> *''[[Triops longicaudatus]]'' <small>([[John Lawrence LeConte|LeConte]], 1846)</small> *''[[Triops numidicus]]'' *''[[Triops newberryi]]'' <small>([[John Lawrence LeConte|LeConte]], 1846)</small> ==Geological history== Another notable characteristic of tadpole shrimps is their unusual geological longevity. The living species ''Triops cancriformis'' has been found fossilized in [[Triassic]] [[Stratum|strata]] of [[Germany]]. A detailed analysis of the traces of the crustaceans and their appendages concluded that the Triassic tadpole shrimp is nearly identical to modern ones. It inhabited the same type of pools that modern notostracans inhabit. Modern African species had also been found fossilized, but those were found in [[Jurassic]] and more recent strata. No other living animal species is known to have existed so long ago. Tadpole shrimps are quite rightfully referred to as "[[living fossil]]s". <ref>L. A. Zenkevich. ''The Animal Life (Zhizn' Zhivotnykh), Volume 2. Chapter 7 - Phylum Arthropoda.''</ref> ==Notostracans in the aquarium== Notostracans, primarily ''Triops longicaudatus'', are often sold to children in small packets as eggs as an interesting science project or as a beginner's kit for their first [[aquarium]].They first have to keep the triops in water at a temperature of 22-29 degrees celsius. One then pours distilled or spring water onto the eggs, and they will hatch out very quickly--often within less than a day. They will also grow at a remarkable pace; growth is actually noticeable from one day to the next until they reach their maximum size of approximately 2 inches, including their caudal appendages. If food is not available in plenty--and sometimes even if it is--they will not hesitate to eat each other. These creatures can make a useful addition to a freshwater aquarium, as they keep the substrate very clean and eat almost anything they find. They may, however pose a slight danger to very small fish or other crustaceans, and may in turn be eaten by large fish. Also, they may damage the roots of aquarium plants they encounter if not kept well fed. They are also very short-lived pets, but are easily replaceable. By thoroughly drying the tank in which they are kept after a die-off and then allowing the completely dry tank to sit for at least a month and finally reflooding it with distilled or spring water, another generation of pets is easily generated, as the previous brood will have left eggs in the substrate. This simulates the periodic drying and flooding of the natural habitat of the tadpole shrimp. ==Related Articles== *[[Triop Kingdom]], where people may hatch triops in their own home. ==References== {{reflist}} == External links == * [http://www.billabongbugs.com Billabong Bugs Home Page] *[http://mytriops.com MyTriops.com] *[http://www.arkive.org/species/ARK/invertebrates_terrestrial_and_freshwater/Triops_cancriformis/ ARKive - images and movies of the tadpole shrimp (''Triops cancriformis'')] *[http://www.kandarian.com/son/ScienceFair.html Triops Science Fair Project] *[http://www.thinkgeek.com/geektoys/science/75ab/ Purchase a Triops Kit!] *{{ITIS|ID=83756|taxon=Notostraca|year=2007|date=22 May}} {{commonscat|Notostraca}} [[Category:Branchiopoda]] [[Category:Living fossils]] [[Category:Freshwater crustaceans]] [[ca:Tortugueta]] [[da:Damrokker]] [[es:Notostraca]] [[fr:Triopsidae]] [[it:Notostraca]] [[lt:Skydvėžiai]] [[ja:カブトエビ]] [[no:Skjoldkreps]] [[nn:Skjoldkreps]] [[pl:Przekopnice]] [[ru:Щитни]] [[simple:Tadpole shrimp]] [[fi:Notostraca]] [[sv:Sköldbladfotingar]] [[tr:Triops]] [[uk:Щитні]]