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Dendrobranchiata is a suborder of Decapoda, commonly known as prawns (though this may be ambiguous). 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 (hence their scientific name ) 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 and a mass of , and are widely shrimp fishery and shrimp farm for human consumption.
Due to their superficial similarity, Dendrobranchiata and Caridea were historically grouped together, though it is currently understood that they are distantly related. The classification of these groups is explained below.
As well as the three pairs of maxillipeds, the thorax also bears five pairs of , or walking legs; the first three of these end in small chelae (pincers).Tavares & Martin, 2010, pp. 108–110 The last two pereiopods are absent in Luciferidae and Acetes, but much longer than the preceding pereiopods in Hymenopenaeus and Xiphopenaeus.Tavares & Martin, 2010, p. 110
The thoracic appendages carry , which are protected beneath the carapace.Tavares & Martin, 2010, pp. 103–105 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).Tavares & Martin, 2010, p. 103
The nervous system of prawns comprises a dorsal brain, and a ventral nerve cord, connected by two around the oesophagus.Tavares & Martin, 2010, p. 114 The chief sensory inputs are visual input from the eyes, on the antennae and in the mouth, and on the antennae and elsewhere.Tavares & Martin, 2010, pp. 116–118
The digestive system comprises a foregut, a midgut and a hindgut, and is situated dorsally.Tavares & Martin, 2010, p. 118 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 are released, and nutrients taken up. The hindgut forms faecal pellets, which are then passed out through the muscular anus.Tavares & Martin, 2010, pp. 118–119
The circulatory system is based around a compact, triangular heart, which pumps blood into three main artery.Tavares & Martin, 2010, p. 120 Excretion is carried out through the gills, and by specialised located at the base of the antennae, and is mostly in the form of ammonia.Tavares & Martin, 2010, pp. 120–121
With the exception of Luciferidae, the eggs of prawns are shed directly into the water, rather than being brooded.Tavares & Martin, 2010, p. 130 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 ecdysis are gradual, and so the development is anamorphic rather than metamorphosis.
Uniquely among the Decapoda, the nauplii of Dendrobranchiata are free-swimming. There are five to eight naupliar stages.Tavares & Martin, 2010, p. 131 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 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 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 have appeared.
By the mysis stages, the (thoracic appendages) start to be used instead of the antennae for locomotion.Tavares & Martin, 2010, p. 133 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 have appeared on the first five segments of the abdomen.
The post-larva or juvenile stage is characterised by the use of the pleopods for locomotion.Tavares & Martin, 2010, p. 134 The claws become functional, but the 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.
The cladogram below shows Dendrobranchiata's placement within the larger order Decapoda, from analysis by Wolfe et al., 2019.
Before 2010, the earliest known fossil prawns come from rocks in Madagascar of Permian-Triassic age, .Crean, 2004Schram et al., 2000 In 2010, however, the discovery of Aciculopoda from Famennian–stage rocks in Oklahoma extended the group's fossil record back to .Feldmann & Schweitzer, 2010 The best known fossil prawns are from the Jurassic Solnhofen limestones from Germany.
Living prawns are divided among seven families, five in the superfamily Penaeoidea, and two in the Sergestoidea, although molecular evidence disagrees with some aspects of the current classifications.Ma et al., 2009 Collectively, these include 540 extant taxon species, and nearly 100 exclusively fossil species.De Grave et al., 2009 A further two families are known only from fossils.
The cladogram below shows Dendrobranchiata's internal relationships of extant taxon families (excluding Solenoceridae):
Prawns are "opportunistic omnivores", and their diet can include a range of food items from fine particles to large organisms. These may include fish, , krill, , , phytoplankton, , and detritus.Tavares & Martin, 2010, p. 135 Prawns eat less around the time of ecdysis (moulting), probably because of the softness of the mouthparts, and must eat more than usual to compensate, once ecdysis is complete.
Prawns are an attractive food for , with a higher energy content than most other invertebrates.Dall, 1990, p. 357 The larvae are prey to comb jelly, jellyfish, , fish and other (such as mantis shrimp and ), and only a tiny proportion survive.Dall, 1990, p. 358 Juveniles are targeted by a number of fish, and ; Litopenaeus vannamei juveniles experience 90% mortality in the 6–12 weeks they spend in Mexican , and this is thought to be due almost entirely to predation. Adult prawns are less susceptible to predation, but can fall prey to some fish.Dall, 1990, p. 359
Species from the family Aristeidae are important to deep-water fisheries, particularly in the Mediterranean Sea, where Aristaeomorpha foliacea is caught by trawlers. In Brazil, Aristaeomorpha foliacea, Aristaeopsis edwardsiana and Aristeus antillensis are of commercial importance. The shallow-water Penaeidae are of greater importance, however, and the most important species for fisheries is Fenneropenaeus chinensis, with a catch in 2005 of over 100,000 tons.
The most important species for aquaculture are Marsupenaeus japonicus (Kuruma prawn), Fenneropenaeus chinensis (Chinese prawn), Penaeus monodon (giant tiger prawn) and Litopenaeus vannamei (whiteleg prawn).
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