46-465: Dendrobranchiata Pleocyemata See text for superfamilies. The Decapoda or decapods ( lit. ' ten-footed ' ) are an order of crustaceans within the class Malacostraca , and includes crabs , lobsters , crayfish , shrimp , and prawns . Most decapods are scavengers . The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with
92-541: A cephalothorax (head and thorax fused together) and a pleon (abdomen). The body is generally slightly flattened side-to-side. The largest species, Penaeus monodon , can reach a mass of 450 grams (16 oz) and a length of 336 millimetres (13.2 in). The most conspicuous appendages arising from the head are the antennae . The first pair are biramous (having two flagella ), except in Luciferidae , and are relatively small. The second pair can be 2–3 times
138-717: A phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
184-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
230-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
276-488: A mass of 450 grams (1.0 lb), and are widely fished and farmed for human consumption. While Dendrobranchiata and Caridea belong to different suborders of Decapoda , they are very similar in appearance, and in many contexts such as commercial farming and fisheries , they are both often referred to as "shrimp" and "prawn" interchangeably. In the United Kingdom , Australia and some other Commonwealth ,
322-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
368-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
414-474: A two-lobed telson , and the beginnings of a carapace emerge at this stage. There are typically five or six zoea stages in Dendrobranchiata, divided into protozoea and mysis. In the protozoea larvae, the antennae are still used for locomotion, but the mandibles become specialised for mastication . All the thoracic somites (body segments) have formed, and a carapace is present, covering part of
460-491: Is anamorphic rather than metamorphic . Uniquely among the Decapoda, the nauplii of Dendrobranchiata are free-swimming. There are five to eight naupliar stages. The earlier stages have three pairs of appendages that are used for locomotion – two pairs of antennae and the mandibles . Later stages also have rudiments of other mouthparts , but the nauplius is unable to feed, and only lasts 24 to 68 hours. The body ends at
506-482: 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
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#1732773082647552-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
598-424: Is characterised by the use of the pleopods for locomotion. The claws become functional, but the gills are still rudimentary. The telson is narrower and only retains traces of its two-lobed development. Through a series of gradual changes over following moults, the animal takes on its adult form. Dendrobranchiata were traditionally grouped together with Caridea as "Natantia" (the swimming decapoda), as opposed to
644-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
690-713: Is only as long as the stalked eyes in Benthesicymidae , Luciferidae and Sergestidae , but considerably longer in Aristeidae . As well as the three pairs of maxillipeds, the thorax also bears five pairs of pereiopods , or walking legs; the first three of these end in small chelae (pincers). The last two pereiopods are absent in Luciferidae and Acetes , but much longer than the preceding pereiopods in Hymenopenaeus and Xiphopenaeus . The thoracic appendages carry gills , which are protected beneath
736-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
782-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
828-509: The Antarctic Ocean . There is a great deal of ecological variation within the suborder Dendrobranchiata. Some species of Sergestidae live in fresh water , but most prawns are exclusively marine. Species of Sergestidae and Benthesicymidae mostly live in deep water, and Solenoceridae species live offshore, while most Penaeidae species live in shallow inshore waters, and Lucifer is planktonic . Some species burrow in mud on
874-498: The Reptantia (the walking decapods). In 1888, Charles Spence Bate recognised the differences in gill morphology, and separated Natantia into Dendrobranchiata, Phyllobranchiata and Trichobranchiata. Recent analyses using cladistics and molecular phylogenetics recognise Dendrobranchiata as the sister group to all other Decapoda, collectively called Pleocyemata . The cladogram below shows Dendrobranchiata's placement within
920-408: The caridoid escape reaction . These muscles, collectively, are the meat for which prawns are commercially fished and farmed. The nervous system of prawns comprises a dorsal brain , and a ventral nerve cord , connected by two commissures around the oesophagus . The chief sensory inputs are visual input from the eyes, chemoreceptors on the antennae and in the mouth, and mechanoreceptors on
966-408: The pereiopods , found on the last five thoracic segments. In many decapods, one pair of these "legs" has enlarged pincers, called chelae , with the legs being called chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts , antennae, and antennules. There are five more pairs of appendages on
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#17327730826471012-609: The superfamily Penaeoidea , and two in the Sergestoidea , although molecular evidence disagrees with some aspects of the current classifications. Collectively, these include 540 extant species, and nearly 100 exclusively fossil species. A further two families are known only from fossils. The cladogram below shows Dendrobranchiata's internal relationships of extant families (excluding Solenoceridae ): Luciferidae Sergestidae Sicyoniidae Penaeidae Benthesicymidae Aristeidae Dendrobranchiata comprises
1058-552: The "white shrimp", Litopenaeus setiferus . The Pleocyemata include the remaining groups, including "true shrimp". Those groups that usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia. This classification to the level of superfamilies follows De Grave et al. Order Decapoda Latreille, 1802 [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Dendrobranchiata Penaeoidea Sergestoidea Penaeidea Dana, 1852 Dendrobranchiata
1104-551: The abdomen. They are called pleopods . There is one final pair called uropods , which, with the telson , form the tail fan. A 2019 molecular clock analysis suggested decapods originated in the Late Ordovician around 455 million years ago, with the Dendrobranchiata (prawns) being the first group to diverge. The remaining group, called Pleocyemata , then diverged between the swimming shrimp groupings and
1150-448: The antennae and elsewhere. The digestive system comprises a foregut, a midgut and a hindgut, and is situated dorsally. The foregut begins at the mouth, passes through the oesophagus, and opens into a sac that contains the grinding apparatus of the gastric mill . The hepatopancreas feeds into the midgut, where digestive enzymes are released, and nutrients taken up. The hindgut forms faecal pellets, which are then passed out through
1196-638: The carapace. The gills are typically branched, and so resemble trees, lending the group its scientific name, Dendrobranchiata, from the Greek words δένδρον ( dendron , tree ) and βράγχια ( branchia , gills). The pleon , or abdomen, is similar in length to the cephalothorax. It has six segments, the first five bearing lamellar pleopods , and the last one bearing uropods . The pleopods are biramous, except in Sicyoniidae , where they are uniramous. The uropods and telson collectively form
1242-481: The cladogram above, the clade Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the sister clade to Polychelida , within Reptantia . Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata . The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as
1288-545: The crawling/walking group called Reptantia , consisting of lobsters and crabs . High species diversification can be traced to the Jurassic and Cretaceous periods, which coincides with the rise and spread of modern coral reefs , a key habitat for the decapods. Despite the inferred early origin, the oldest fossils of the group such as Palaeopalaemon only date to the Late Devonian . The cladogram below shows
1334-627: The earliest known fossil prawns come from rocks in Madagascar of Permo - Triassic age, 250 million years ago . In 2010, however, the discovery of Aciculopoda from Famennian –stage rocks in Oklahoma extended the group's fossil record back to 360 million years ago . The best known fossil prawns are from the Jurassic Solnhofen limestones from Germany . Living prawns are divided among seven families, five in
1380-497: The following superfamilies and families : The biodiversity of Dendrobranchiata decreases markedly at increasing latitudes ; most species are only found in a region between 40° north and 40° south . Some species may occur at higher latitudes. For instance, Bentheogennema borealis is abundant at 57° north in the Pacific Ocean , while collections of Gennadas kempi have been made as far south as 61° south in
1426-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
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1472-630: The internal relationships of Decapoda, from analysis by Wolfe et al. (2019). Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] In
1518-638: The larger order Decapoda , from analysis by Wolfe et al. , 2019. Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] Before 2010,
1564-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
1610-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
1656-417: The length of the body and are always uniramous (having a single flagellum). The mouthparts comprise pairs of mandibles , maxillules and maxillae, arising from the head, and three pairs of maxillipeds, arising from the thorax. A pair of stalked eyes points forwards from the head. The carapace grows from the thorax to cover the cephalothorax, and extends forwards between the eyes into a rostrum . This
1702-402: The moulting cycle, and usually occurs at night. With the exception of Luciferidae , the eggs of prawns are shed directly into the water, rather than being brooded. The eggs hatch into nauplius larvae , which are followed by zoea larvae (initially protozoea, and later mysis) and then a postlarva, before reaching adulthood. The changes between moults are gradual, and so the development
1748-420: The muscular anus . The circulatory system is based around a compact, triangular heart , which pumps blood into three main arteries . Excretion is carried out through the gills, and by specialised glands located at the base of the antennae, and is mostly in the form of ammonia . Prawns may be divided into two groups: those with an open thelycum (female genitalia) and those with a closed thelycum. In
1794-447: The mysis stages, the pereiopods (thoracic appendages) start to be used instead of the antennae for locomotion. The larva swims backwards, with its tail upwards, spinning slowly as it goes. The carapace covers most of the segments of the thorax, and claws appear on the first three pereiopods. By the last mysis stage, the beginnings of pleopods have appeared on the first five segments of the abdomen. The post-larva or juvenile stage
1840-549: The open–thelycum species, mating takes place towards the end of the moulting cycle, and usually at sunset. In closed–thelycum species, mating takes place shortly after moulting, when the exoskeleton is still soft, and usually occurs in the night. Courtship and mating may take up to 3 hours in Penaeus monodon , while in Farfantepenaeus paulensis , mating lasts just 4–5 seconds. Spawning may occur several times during
1886-407: The sea floor during the day and emerge at night to feed. Prawns are "opportunistic omnivores", and their diet can include a range of food items from fine particles to large organisms. These may include fish , chaetognaths , krill , copepods , radiolarians , phytoplankton , nematocysts , ostracods and detritus . Prawns eat less around the time of ecdysis (moulting), probably because of
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1932-486: The shrimp (about 3,000 species) and Anomura including hermit crabs , porcelain crabs , squat lobsters (about 2500 species) making up the bulk of the remainder. The earliest fossils of the group date to the Devonian . Decapods can have as many as 38 appendages, arranged in one pair per body segment. As the name Decapoda (from the Greek δέκα , deca- , "ten", and πούς / ποδός , -pod , "foot") implies, ten of these appendages are considered legs. They are
1978-419: The softness of the mouthparts, and must eat more than usual to compensate, once ecdysis is complete. Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on
2024-429: The tail fan; the uropods are not divided by a diaeresis, as they are in many other decapods. The telson is pointed and is usually armed with four pairs of setae or spines . Most of the musculature of a prawn is used for bending the pleon, and almost all the space in the pleon is filled by muscle. More than 17 muscles operate each of the pleopods, and a further 16 power the tail fan in the rapid backward movement of
2070-427: The thorax. It is smooth in the family Penaeidae , but bears many spines in the family Solenoceridae . The pleon (abdomen) is unsegmented in the first protozoea, and ends in a bilobed telson, which may be used for cleaning other appendages, or for steering. By the second protozoea, segmentation appears on the pleon, and by the third protozoea, which may also be called the metazoea, the uropods have appeared. By
2116-505: The word "prawn" is used almost exclusively, while the opposite is the case in North America . The term "prawn" is also loosely used to describe any large shrimp, especially those that come 15 (or fewer) to the pound (such as "king prawns", yet sometimes known as "jumbo shrimp"). Together with other swimming Decapoda, Dendrobranchiata show the "caridoid facies", or shrimp-like form. The body is typically robust, and can be divided into
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