Pleocyemata is a sub-order of decapod

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...

 crustaceans

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...

, erected by Martin Burkenroad in 1963. Burkenroad's classification replaced the earlier sub-orders of Natantia

Natantia

Natantia is an obsolete taxon of decapod crustaceans, comprising those families that move predominantly by swimming – the shrimp, prawns and boxer shrimp. The remaining Decapoda were placed in the Reptantia, and consisted of crabs, lobsters and other large animals that move chiefly by walking along...

 and Reptantia with the monophyletic groups Dendrobranchiata (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) and Pleocyemata. Pleocyemata contains all the members of the Reptantia (including crabs, lobsters, crayfish, and others), as well as 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...

 (which contains the so-called "boxer shrimp" or "barber-pole shrimp"), and Caridea

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...

, which contains all the true shrimp. Pleocyemata comprises the following infraorders:

• 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...
  
  
• Caridea
• Astacidea
  Astacidea
  Astacidea is a group of decapod crustaceans including lobsters, crayfish and their close relatives. It comprises five extant superfamilies, two of crayfish , one of true lobsters , one of reef lobsters , and a number of fossil taxa...
  
  
• Glypheidea
  Glypheidea
  Glypheidea is an infra-order of decapod crustaceans, comprising a number of fossil forms and the two extant genera Neoglyphea and Laurentaeglyphea:Glypheoidea Winckler, 1882*† Chimaerastacidae Amati, Feldmann & Zonneveld, 2004...
  
  
• Axiidea
• Gebiidea
• Achelata
  Achelata
  The Achelata is an infra-order of the reptant Decapoda. It contains the spiny lobsters , the slipper lobsters and the furry lobsters...
  
  
• Polychelida
  Polychelida
  Polychelida is a group of decapod crustaceans. Fossil representatives are known dating from as far back as the Upper Triassic. A total of 38 extant species, all in the family Polychelidae, and 55 fossil species have been described....
  
  
• 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;...
  
  
• Brachyura
  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...
  
  

These taxa are united by a number of features, the most important of which is that the fertilised

Fertilisation

Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...

 eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 are incubated by the female, and remain stuck to the pleopods (swimming legs) until they are ready to hatch. It is this characteristic that gives the group its name.

The earliest fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 representative is the Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 Palaeopalaemon.