Eucarida
Encyclopedia
Eucarida is a superorder of the Malacostraca
, a class of the crustacean subphylum, comprising the decapods
, krill
and Amphionides
. They are characterised by having the carapace
fused to all thoracic
segments, and by the possession of stalked eyes.
and are all marine shrimp-like species whose pleopods (abdominal appendages) function as swimmerets, they swarm and mostly feed on plankton
, this group is composed of only 90 species, but some of these are one of the most abundant species on the planet, in fact, it is estimated that the biomass of the Antarctic krill
Euphausia superba is 500 million tons.
s (which are exposed in krill). They include lobster
s, crab
s, shrimp
and prawn
s. The decapods are further subdivided on the basis of the gill structure into two suborders Dendrobranchiata (prawns) and Pleocyemata
, which is further subdivided into several infraorders, such as the Caridea (true shrimps), the Stenopodidea
(boxer shrimp) and the Anomura
and the Brachyura (crab
s) and so forth.
of Eucarida is also under question:
Malacostraca
Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...
, a class of the crustacean subphylum, comprising the decapods
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
, krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
and Amphionides
Amphionides
Amphionides reynaudii is the sole representative of the order Amphionidacea, and is a small planktonic crustacean found throughout the world's tropical oceans, mostly in shallow waters.-Description:...
. They are characterised by having the carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
fused to all thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
segments, and by the possession of stalked eyes.
Euphausiacea
The members of the Euphausiacea are commonly called krillKrill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
and are all marine shrimp-like species whose pleopods (abdominal appendages) function as swimmerets, they swarm and mostly feed on plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, this group is composed of only 90 species, but some of these are one of the most abundant species on the planet, in fact, it is estimated that the biomass of the Antarctic krill
Antarctic krill
Antarctic krill, Euphausia superba, is a species of krill found in the Antarctic waters of the Southern Ocean. It is a shrimp-like crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre...
Euphausia superba is 500 million tons.
Decapoda
The Decapoda is a group with 15,000 species which have 5 pairs of thoracopods and a well-developed carapace that covers the gillGill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s (which are exposed in krill). They include lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
and prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s. The decapods are further subdivided on the basis of the gill structure into two suborders Dendrobranchiata (prawns) and Pleocyemata
Pleocyemata
Pleocyemata is a sub-order of decapod crustaceans, erected by Martin Burkenroad in 1963. Burkenroad's classification replaced the earlier sub-orders of Natantia and Reptantia with the monophyletic groups Dendrobranchiata and Pleocyemata...
, which is further subdivided into several infraorders, such as the Caridea (true shrimps), the Stenopodidea
Stenopodidea
The Stenopodidea is a small group of decapod crustaceans. Often confused with shrimp or prawns, they are neither, but belong in a group closer to the reptant decapods, such as lobsters and crabs. They may be easily recognised by their third pereiopod , which is greatly enlarged...
(boxer shrimp) and the Anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
and the Brachyura (crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s) and so forth.
Amphionidacea
In addition, there is an enigmatic eucarid species, Amphionides reynaudii, which is the sole representative of its order, but due to the loss of several features resulting from its small size, its classification has been unclear.Phylogeny
The phylogeny of the Malacostraca is debated. In particular, the monophylyMonophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
of Eucarida is also under question:
- Monophyletic: many argue that the Eucarida group is a cladeCladeA clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, sister to the Peracarida clade or to the basal Malacostraca. or to Mysida (paraphyletic Schizopoda) - Paraphyletic: some have proposed a paraphyletic Eucarida forming a clade with a nested Peracarida.
- Polyphyletic: some have grouped Euphausiacea with Mysida to form the SchizopodaSchizopodaSchizopoda is a former taxonomical classification of a division of the class Malacostraca. Although it was split in 1883 by Johan Erik Vesti Boas into the two distinct orders Mysidacea and Euphausiacea, the order Schizopoda continued to be in use until the 1930s....
, or the Euphausiacea with the Hoplocarida, with Decapoda basal to the Peracarida.