Malacostraca

Malacostraca

Overview
Malacostraca is the largest of the six classes
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 of crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, containing over 25,000 extant species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, divided among 16 orders
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

. Its members display a greater diversity of body forms than any other class of animals, and include 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, 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, 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...

, 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...

, woodlice
Woodlouse
A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...

, scuds (Amphipoda
Amphipoda
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...

), mantis shrimp
Mantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...

 and many other less familiar animals. They are abundant in all marine environments and have also colonised freshwater and terrestrial habitats. They are united by a common , comprising 20 body segments (rarely 21), divided into a head, thorax and abdomen.


Malacostracans live in a wide range of marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 habitats, and three orders have terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 members: Amphipoda (Talitridae
Talitridae
Talitridae is a family of amphipods. Commonly, many of the North American fresh water species of this family are called scuds. Terrestrial species are often referred to as landhoppers and beach dwellers are called sandhoppers or sand fleas.It contains the following genera:*Africorchestia Lowry &...

), Isopoda (Oniscidea, the woodlice
Woodlouse
A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...

) and Decapoda (terrestrial hermit crabs
Coenobitidae
Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera:*Coenobita Latreille, 1829*Coenobita brevimanus Dana, 1852*Coenobita carnescens Dana, 1851...

, 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 of the families Ocypodidae
Ocypodidae
Ocypodidae is a family of crabs that includes the ghost crabs and fiddler crabs. Other genera previously included in the family are now treated as members of separate families in the superfamily Ocypodoidea, such as Ucididae, Dotillidae and Macrophthalmidae....

, Gecarcinidae and Grapsidae
Grapsidae
Grapsidae is a family of crabs known variously as marsh crabs, shore crabs or talon crabs. It is not confirmed that the family forms a monophyletic group and some taxa may belong in other families...

, and terrestrial crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

).
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Encyclopedia
Malacostraca is the largest of the six classes
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 of crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, containing over 25,000 extant species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, divided among 16 orders
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

. Its members display a greater diversity of body forms than any other class of animals, and include 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, 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, 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...

, 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...

, woodlice
Woodlouse
A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...

, scuds (Amphipoda
Amphipoda
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...

), mantis shrimp
Mantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...

 and many other less familiar animals. They are abundant in all marine environments and have also colonised freshwater and terrestrial habitats. They are united by a common , comprising 20 body segments (rarely 21), divided into a head, thorax and abdomen.

Ecology



Malacostracans live in a wide range of marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 habitats, and three orders have terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 members: Amphipoda (Talitridae
Talitridae
Talitridae is a family of amphipods. Commonly, many of the North American fresh water species of this family are called scuds. Terrestrial species are often referred to as landhoppers and beach dwellers are called sandhoppers or sand fleas.It contains the following genera:*Africorchestia Lowry &...

), Isopoda (Oniscidea, the woodlice
Woodlouse
A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...

) and Decapoda (terrestrial hermit crabs
Coenobitidae
Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera:*Coenobita Latreille, 1829*Coenobita brevimanus Dana, 1852*Coenobita carnescens Dana, 1851...

, 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 of the families Ocypodidae
Ocypodidae
Ocypodidae is a family of crabs that includes the ghost crabs and fiddler crabs. Other genera previously included in the family are now treated as members of separate families in the superfamily Ocypodoidea, such as Ucididae, Dotillidae and Macrophthalmidae....

, Gecarcinidae and Grapsidae
Grapsidae
Grapsidae is a family of crabs known variously as marsh crabs, shore crabs or talon crabs. It is not confirmed that the family forms a monophyletic group and some taxa may belong in other families...

, and terrestrial crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

). They are abundant in all marine ecosystems, and most species are scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...

s, although some, such as the porcelain crab
Porcelain crab
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices...

s, are filter feeder
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

s, and some, such as mantis shrimp
Mantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...

, are carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

s.

Etymology


The name Malacostraca comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 roots
Root (linguistics)
The root word is the primary lexical unit of a word, and of a word family , which carries the most significant aspects of semantic content and cannot be reduced into smaller constituents....

  (, meaning "soft") and (, meaning "shell"). The name is misleading, since the shell is only soft immediately after moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...

, and is usually hard. Malacostracans are sometimes contrasted with entomostracans, a name applied to all crustaceans outside the Malacostraca, and named after the obsolete taxon Entomostraca
Entomostraca
Entomostraca is a historical subclass of Crustacea, no longer in technical use. It was originally considered one of the two major lineages of crustaceans , combining all other classes – Branchiopoda, Cephalocarida, Ostracoda and Maxillopoda. The Ostracoda have the body enclosed in a bivalve...

.

Description



The Class Malacostraca includes over 25,000 species, and "arguably ... contains a greater diversity of body forms than any other class in the animal kingdom". Its members are characterised by the presence of three tagmata – a five-segmented head, an eight-segmented thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 and an abdomen with six segments, except in the Leptostraca
Leptostraca
Leptostraca is an order of small, marine crustaceans. Its members, including the well-studied Nebalia, occur throughout the world's oceans and are usually considered to be filter-feeders. It is the only extant order in the subclass Phyllocarida...

, which retain the ancestral condition of seven abdominal segments. This arrangement is known as the "caridoid facies", a term coined by William Thomas Calman
William Thomas Calman
William Thomas Calman was a Scottish zoologist, specialising in the Crustacea.He was born in Dundee, studying at the High School. In the scientific societies in the city, he met D'Arcy Thompson. He later became Thompson's lab boy, which allowed him to attend lectures at University College, Dundee...

 in 1909. Each body segment bears a pair of jointed appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s, although these may be lost secondarily.

Tagmata


The head bears two pairs of antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

, the first of which is biramous and the second uniramous, and two pairs of maxillae. There is usually a pair of stalked compound eyes, although these may be sessile, reduced or lost.

Up to eight thoracic segments may be fused with the head to form a cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

, and up to three pairs of appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s may be modified as maxillipeds (accessory mouthparts). A 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...

 may be absent, present, or secondarily lost, and may cover from two thoracic segments to the entire thorax and some of the abdomen.

Each segment of the abdomen except the last carries a pair of pleopods. The appendages of the last segment are typically flattened into uropods, which together with the terminal telson
Telson
The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...

, make up the "tail fan". In Leptostraca, these appendages instead form caudal rami
Caudal ramus
The caudal ramus is a characteristic feature of primitive crustaceans. Located on the anal somite , the caudal ramus is a pair of appendage-like or spine-like protrusions. Specific structures which are rod or blade-like are referred to as caudal furca....

.

Life cycle


Most malacostracans are gonochoristic
Gonochorism
In biology, gonochorism or unisexualism describes sexually reproducing species in which individuals have just one of at least two distinct sexes. The term is most often used with animals . The sex of an individual may change during its lifetime, this can for example be found in parrotfish...

 (i.e., they have separate sexes), although there are a few hermaphroditic
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...

 species. The female genital openings are on the sixth thoracic segment, while the male genital opening is usually on the sixth thoracic segment, but is occasionally on the seventh. Each of the thoracic appendages is biramous and also carries a gill
Gill
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...

. The larval stages
Crustacean larvae
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...

 are often reduced, but where they occur, there is usually a metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...

 between the larval and the adult form.

Classification


Martin and Davis present the following classification of living malacostracans into orders, to which extinct orders have been added, indicated by an obelisk
Dagger (typography)
A dagger, or obelisk. is a typographical symbol or glyph. The term "obelisk" derives from Greek , which means "little obelus"; from meaning "roasting spit"...

 (†).



Class Malacostraca Latreille
Pierre André Latreille
Pierre André Latreille was a French zoologist, specialising in arthropods. Having trained as a Roman Catholic priest before the French Revolution, Latreille was imprisoned, and only regained his freedom after recognising a rare species he found in the prison, Necrobia ruficollis...

, 1802
  • Subclass Phyllocarida
    Phyllocarida
    Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca....

     Packard, 1879
  • † Archaeostraca Claus 1888
  • † Hoplostraca Schram, 1973
  • Canadaspidida
    Canadaspis
    Canadaspis was a Cambrian genus of crustacean or euarthropod, a benthic feeder that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food...

     Novožilov in Orlov, 1960
  • Hymenostraca
    Hymenocaris
    Hymenocaris is a genus of Cambrian crustaceans. Some species originally assigned to Hymenocaris were later transferred to Canadaspis, such as Canadaspis perfecta , leaving only Hymenocaris vermicauda...

     Rolfe, 1969
  • Leptostraca
    Leptostraca
    Leptostraca is an order of small, marine crustaceans. Its members, including the well-studied Nebalia, occur throughout the world's oceans and are usually considered to be filter-feeders. It is the only extant order in the subclass Phyllocarida...

     Claus, 1880
  • Subclass Hoplocarida
    Hoplocarida
    Hoplocarida is a subclass of crustaceans. The only extant members are the mantis shrimp , but two other orders existed in the Palaeozoic: Aeschronectida and Palaeostomatopoda....

     Calman, 1904
  • Aeschronectida
    Aeschronectida
    Aeschronectida is an extinct order of mantis shrimp-like crustaceans ....

     Schram, 1969
  • † Archaeostomatopoda Schram, 1969
  • Stomatopoda Latreille, 1817
  • Subclass Eumalacostraca
    Eumalacostraca
    The Eumalacostraca are a subclass of crustaceans, containing almost all living malacostracans, about 40,000 described species. The remaining subclasses are the Phyllocarida and possibly the Hoplocarida or mantis shrimps....

     Grobben, 1892
    • Superorder Syncarida
      Syncarida
      Syncarida is a superorder of crustaceans, comprising the two orders Anaspidacea and Bathynellacea. Fifty-nine genera are known, in six families:Anaspidacea Calman, 1904*Anaspididae Thomson, 1893*Koonungidae Sayce, 1908*Psammaspididae Schminke, 1974...

       Packard, 1885
      • † Palaeocaridacea Brooks, 1979
      • Bathynellacea
        Bathynellacea
        Bathynellacea is an order of crustaceans which live interstitially in groundwater. Some species can tolerate low salt concentrations, and at least one African species is a thermophile, living in hot springs and tolerating temperatures up to . Bathynellaceans are minute, blind, worm-like animals...

         Chappuis, 1915
      • Anaspidacea
        Anaspidacea
        Anaspidacea is an order of crustaceans, comprising eleven genera in four families. Species in the family Anaspididae vary from being strict stygobionts to species living in lakes, streams and moorland pools, and are found only in Tasmania...

         Calman, 1904
    • Superorder Peracarida
      Peracarida
      The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or marsupium, formed from thin flattened plates borne on the basalmost segments of the legs Other...

       Calman, 1904
      • Spelaeogriphacea
        Spelaeogriphacea
        Spelaeogriphacea is an order of crustaceans that grow to no more than . Little is known about the ecology of the order.Only four species, all subterranean, have been described...

         Gordon, 1957
      • Thermosbaenacea
        Thermosbaenacea
        Thermosbaenacea is a group of crustaceans that live in thermal springs in fresh water, brackish water and anchialine habitats. They have occasionally been treated as a distinct superorder , but are generally considered to belong to the Peracarida...

         Monod, 1927
      • Lophogastrida
        Lophogastrida
        Lophogastrida is an order of malacostracan crustaceans in the superorder Peracarida. They are shrimp-like animals that mostly inhabit the relatively deep pelagic waters of the oceans throughout the world....

         Sars, 1870
      • Mysida Haworth, 1825
      • Mictacea
        Mictacea
        Mictacea is the most recently established order of crustaceans, erected for five species of small shrimp-like animals of the deep sea and anchialine caves.-Description:...

         Bowman et al., 1985
      • Amphipoda
        Amphipoda
        Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...

         Latreille, 1816
      • Isopoda
        Isopoda
        Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...

         Latreille, 1817
      • Tanaidacea
        Tanaidacea
        The crustacean order Tanaidacea make up a minor group within the class Malacostraca. There are about 940 species in this order.-Description:...

         Dana, 1849
      • Cumacea
        Cumacea
        Cumacea is an order of small marine crustaceans, occasionally called hooded shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans.-Anatomy:...

         Krøyer, 1846
    • Superorder Eucarida
      Eucarida
      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....

       Calman, 1904
      • Euphausiacea
        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...

         Dana, 1852
      • Amphionidacea
        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:...

         Williamson, 1973
      • Decapoda
        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...

         Latreille, 1802

Phylogenetics



While the monophyly
Monophyly
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 Malacostraca as a whole is widely supported, a number of problems make it difficult to determine the relationships between the orders of Malacostraca. These include differences in rates of evolution
Mutation rate
In genetics, the mutation rate is the chance of a mutation occurring in an organism or gene in each generation...

 in different lineages
Lineage (evolution)
An evolutionary lineage is a sequence of species, that form a line of descent, each new species the direct result of speciation from an immediate ancestral species. Lineages are subsets of the evolutionary tree of life. Lineages are often determined by the techniques of molecular systematics.-...

, different patterns of evolution being apparent in different sources of data, including convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

, and long branch attraction
Long branch attraction
Long branch attraction is a phenomenon in phylogenetic analyses when rapidly evolving lineages are inferred to be closely related, regardless of their true evolutionary relationships. For example, in DNA sequence-based analyses, the problem arises when sequences from two lineages evolve rapidly...

.

Fossil record


The first malacostracans appeared in the Early Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

, when animals belonging to the Phyllocarida
Phyllocarida
Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca....

 appeared.

External links



  • Malacostraca, Tree of Life Web Project
    Tree of Life Web Project
    The Tree of Life Web Project is an ongoing Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world....

  • Introduction to the Malacostraca, University of California, Berkeley
    University of California, Berkeley
    The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

  • "Malacostraca" by Thomas Roscoe Rede Stebbing
    Thomas Roscoe Rede Stebbing
    The Reverend Thomas Roscoe Rede Stebbing F.R.S., F.L.S. was a British zoologist, who described himself as "a serf to natural history, principally employed about Crustacea". Educated in London and Oxford, he only took to natural history in his thirties, having worked as a teacher until then...

    , Encyclopædia Britannica Eleventh Edition
    Encyclopædia Britannica Eleventh Edition
    The Encyclopædia Britannica Eleventh Edition is a 29-volume reference work, an edition of the Encyclopædia Britannica. It was developed during the encyclopaedia's transition from a British to an American publication. Some of its articles were written by the best-known scholars of the time...

  • Malacostraca, The Paleobiology Database
    Paleobiology Database
    ' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...

  • Malacostraca image key - Guide to the marine zooplankton of south eastern Australia, Tasmanian Aquaculture and Fisheries Institute