Notostraca Temporal range: | |
---|---|
Triops australiensis | |
Lepidurus apus | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Branchiopoda |
Superorder: | Calmanostraca |
Order: | Notostraca G. O. Sars, 1867 |
Genera | |
The order Notostraca, containing the single family Triopsidae, is a group of crustaceans known as tadpole shrimp [1] or shield shrimp. [2] The two genera, Triops and Lepidurus , are considered living fossils, with similar forms having existed since the end of the Devonian, around 360 million years ago. They have a broad, flat carapace, which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The telson is flanked by a pair of long, thin caudal rami. Phenotypic plasticity within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are omnivores living on the bottom of temporary pools and shallow lakes.
Notostracans are 2–5 centimetres (0.8–2.0 in) long, with a broad carapace at the front end, and a long, slender abdomen. [1] This gives them a similar overall shape to a tadpole, from which the common name tadpole shrimp derives. [1] The carapace is dorso-ventrally flattened, smooth, and bears no rostrum; it includes the head, and the two sessile compound eyes are located together on top of the head. [1] The two pairs of antennae are much reduced, with the second pair sometimes missing altogether. [2] The mouthparts comprise a pair of uniramous mandibles and no maxillipeds. [2]
The trunk consists of three regions; thorax I, thorax II and the abdomen. Thorax I is made up of 11 segments, each with a pair of well-developed limbs and the genital opening on the eleventh segment. In the female, it is modified to form a "brood pouch". [3] The first one or two pairs of legs differ from the remainder, and probably function as sensory organs. [3]
The somites on thorax II are fused into "rings", which varies in number between species and gender and appear to be body segments, but do not always reflect the underlying segmentation. [1] Each ring is made up of 2–6 complete or partial fused segments, and the number of legs on each body ring match its number of segments. [4] [1] The legs become progressively smaller posteriorly, [3] with the last segments being legless. [1]
The limbless abdomen ends in a telson and a pair of long, thin, multi-articulate caudal rami. [5] The form of the telson varies between the two genera: in Lepidurus , a rounded projection extends between the caudal rami, while in Triops there is no such projection. [1]
Within the Notostraca, and even within species, there is variation in the mode of reproduction, with some populations reproducing sexually, some showing self-fertilisation of females, and some showing a mix of the two. [1] [6] The frequency of males in populations is therefore highly variable. [3] In sexual populations, the sperm leave the male's body through simple pores, there being no penis. The eggs are released by the female and then held in the cup-like brood pouch. [3] The eggs are retained by the female only for a short time before being laid, [7] and the larvae develop directly, without passing through a metamorphosis. [2]
Notostracans are omnivorous, eating small animals such as fishes and fairy shrimp. [1] They are found worldwide in freshwater, brackish water, or saline pools, as well as in shallow lakes, peat bogs, and moorland. [2] The species Triops longicaudatus is considered an agricultural pest in California rice paddies, because it prevents light from reaching the rice seedlings by stirring up sediment. [8]
The fossil record of Notostraca is extensive, occurring in a wide range of geological deposits. [9] The oldest known notostracan is the species Strudops goldenbergi from the Late Devonian (Famennian ~ 365 million years ago) of Belgium. [10] The lack of major morphological change since 250 million years ago has led to Notostraca being described as living fossils. [11] Kazacharthra, a group known only from Triassic and Jurassic fossils from Kazakhstan and Western China, [12] are closely related to notostracans, and may belong within the order Notostraca, [13] or alternatively are placed as their sister group within the clade Calmanostraca.
The "central autapomorphy" of the Notostraca is the abandonment of filter feeding in open water, and the development of a benthic lifestyle in muddy waters, taking up food from particles of sediment and preying on small animals. [7] A number of other characteristics are correlated with this change, including the increased size of the animal compared to its relatives, and the loss of the ability to hinge the carapace; although a central keel marks the former separation into two valves, the adductor muscle is missing. [7] Notostracans retain the plesiomorphic condition of having two separate compound eyes, which abut, but have not become united, as seen in other groups of Branchiopoda. [7]
The extant members of order Notostraca composed a single family, Triopsidae, with only two genera, Triops and Lepidurus . [11] The problematic Middle Ordovician fossil Douglasocaris has been erected and placed in its own family Douglasocaridae by Caster & Brooks 1956, and may be ancestral to Notostraca.
The phenotypic plasticity shown by notostracan species make identification to the species level difficult. [11] Many putative species have been described based on morphological variation, such that by the 1950s, as many as 70 species were recognised. [11] Two important revisions – those of Linder in 1952 [14] and Longhurst in 1955 [15] – synonymised many taxa, and resulted in the recognition of only 11 species in the two genera. This taxonomy was accepted for decades, [11] "even attaining the status of dogma". [16] More recent studies, especially those employing molecular phylogenetics, have shown that the eleven currently recognised species conceal a greater number of reproductively isolated populations. [11]
Incertae sedis species
Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca, Notostraca, the Devonian Lepidocaris and possibly the Cambrian Rehbachiella. They are mostly small, freshwater animals that feed on plankton and detritus.
Dendrobranchiata is a suborder of decapods, commonly known as prawns. There are 540 extant species in seven families, and a fossil record extending back to the Devonian. They differ from related animals, such as Caridea and Stenopodidea, by the branching form of the gills and by the fact that they do not brood their eggs, but release them directly into the water. They may reach a length of over 330 millimetres (13 in) and a mass of 450 grams (1.0 lb), and are widely fished and farmed for human consumption.
Malacostraca is the second largest of the six classes of pancrustaceans behind insects, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobsters, crayfish, shrimp, krill, prawns, woodlice, amphipods, mantis shrimp, tongue-eating lice and many other less familiar animals. They are abundant in all marine environments and have colonised freshwater and terrestrial habitats. They are segmented animals, united by a common body plan comprising 20 body segments, and divided into a head, thorax, and abdomen.
Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in the former order Conchostraca, which later proved to be paraphyletic, because water fleas are nested within clam shrimps. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae.
Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered mountain lakes, and Antarctic ice. They are usually 6–25 mm (0.24–0.98 in) long. Most species have 20 body segments, bearing 11 pairs of leaf-like phyllopodia, and the body lacks a carapace. They swim "upside-down" and feed by filtering organic particles from the water or by scraping algae from surfaces, with the exception of Branchinecta gigas, or "giant fairy shrimp", which is itself a predator of other species of anostracans. They are an important food for many birds and fish, and some are cultured and harvested for use as fish food. There are 300 species spread across 8 families.
Triops is a genus of small crustaceans in the order Notostraca. 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.
Kazacharthra is an extinct order of branchiopod crustaceans that appear to be closely related to the living order Notostraca. Kazacharthrans lived in marshes and ponds in the Upper Triassic of Western China and Mongolia, and in Lower Jurassic Kazakhstan. It is presumed that the kazacharthrids lived much like their living relatives, in that they were opportunistic omnivores that fed on any available food source, from bacterial biofilms to detritus to smaller animals that could be overpowered.
Triops longicaudatus is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flattened shield-like brownish carapace covering two thirds of the thorax, and two long filaments on the abdomen. The genus name Triops comes from Greek ὤψ or ṓps, meaning "eye" prefixed with Latin tri-, "three", in reference to its three eyes. Longicaudatus is a Latin neologism combining longus ("long") and caudatus ("tailed"), referring to its long tail structures. Triops longicaudatus is found in fresh water ponds and pools, often in places where few higher forms of life can exist.
Triops australiensis, sometimes referred to as a shield shrimp, is an Australian species of the tadpole shrimp Triops.
Triops newberryi is a species of Triops found on the western coast of North America, commonly in valleys throughout the states of Washington, Oregon, California, and small areas of Nevada, Utah, New Mexico, and Mexico, with at least one disjunct population in Kansas. They are found in vast numbers though in the Coachella Valley in California. T. newberryi has been reported to have potential as a biocontrol agent for larval mosquitoes breeding in seasonally-flooded habitats. T. newberryi is genetically distinct from T. longicaudatus, the dominant species in the Central United States.
Triops cancriformis, European tadpole shrimp or tadpole shrimp is a species of tadpole shrimp found in Europe to the Middle East and India.
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults, more-so than where the larvae are planktonic, and thereby easily caught.
Chenops is an extinct genus of notostracan which existed in the Yixian Formation, Inner Mongolia, and the Jehol fauna of China during the early Cretaceous period. The genus was erected by Thomas A. Hegna and Ren Dong in 2010 to describe the Yixian species, Chenops yixianensis. A second species, originally described as "Prolepidurus oblongus", from the Jehol fauna, was redescribed as C. oblongus.
Jeholops is an extinct genus of notostracan which existed in the Yixian Formation, inner Mongolia, China during the early Cretaceous period. It was described by Thomas A. Hegna and Ren Dong in 2010, and the only species is Jeholops hongi.
Chirocephalus diaphanus is a widely distributed European species of fairy shrimp that lives as far north as Great Britain, where it is the only surviving species of fairy shrimp and is protected under the Wildlife and Countryside Act 1981. It is a translucent animal, about 0.5 in (13 mm) long, with reddened tips to the abdomen and appendages. The body comprises a head, a thorax bearing 11 pairs of appendages, and a seven-segmented abdomen. In males, the antennae are enlarged to form "frontal appendages", while females have an egg pouch at the end of the thorax.
Lepidocaris rhyniensis is an extinct species of crustacean. It is the only species known from the order Lipostraca, and is the only abundant animal in the Pragian-aged Rhynie chert deposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear. The body is 3 mm (0.12 in) long, with 23 body segments and 19 pairs of appendages, but no carapace. It occurred chiefly among charophytes, probably in alkaline temporary pools.
Crustaceans are invertebrate animals that constitute one group of arthropods that are a part of the subphylum Crustacea, a large, diverse group of mainly aquatic arthropods including decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, opossum shrimps, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods emerged deep in the Crustacean group, with the completed pan-group referred to as Pancrustacea. The three classes Cephalocarida, Branchiopoda and Remipedia are more closely related to the hexapods than they are to any of the other crustaceans.
Lepidurus apus, commonly known as a tadpole shrimp, is a notostracan in the family Triopsidae, one of a lineage of shrimp-like crustaceans that have had a similar form since the Triassic period and are considered living fossils. This species is cosmopolitan, inhabiting temporary freshwater ponds over much of the world, and the most widespread of the tadpole shrimps. Like other notostracans, L. apus has a broad carapace, long segmented abdomen, and large numbers of paddle-like legs. It reproduces by a mixture of sexual reproduction and self-fertilisation of females.
Nodosculda is an extinct genus of mantis shrimp that lived in North America during the late Albian stage of the Early Cretaceous period, between 105 and 100 million years ago. The only species is Nodosculda fisherorum, known from several specimens uncovered in the Paw Paw Formation of Texas.
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