Astacidea is an

infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

of decapod

crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

ns including

lobster Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...

s (though not "lobsters" such as the

spiny lobster Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, S ...

etc.),

crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, ...

, and their close relatives.

Description

The Astacidea are distinguished from most other decapods by the presence of

chelae A chela ()also called a claw, nipper, or pinceris a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds. ...

(claws) on each of the first three pairs of

pereiopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

s (walking legs), the first of which is much larger than the remaining two pairs. The last two pairs of pereiopods are simple (without claws), except in ''

Thaumastocheles The family Thaumastochelidae contains five known species of deep-sea lobsters, three in the genus ''Thaumastocheles'', and two in the genus ''Thaumastochelopsis''. The fifth species was discovered in the ten–year Census of Marine Life. These cr ...

'', where the fifth pereiopod may have "a minute pincer".

Distribution

Members of the infraorder Astacidea are found throughout the world – both in the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

s and in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...

– except for mainland Africa and parts of Asia.

Classification

Astacidea belongs to the group

Reptantia Reptantia is a clade of decapod crustaceans named in 1880 which includes lobsters, crabs and many other well-known crustaceans. Classification In older classifications, Reptantia was one of the two sub-orders of Decapoda alongside Natantia, ...

, which consists of the walking/crawling decapods (lobsters and

crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting " tail" ( abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in al ...

). Astacidea is the

sister clade In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to the infraorder Polychelida, a small group of crustaceans restricted to deep waters. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below shows Astacidea's placement within the larger order

Decapoda The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is es ...

, from analysis by Wolfe ''et al.'', 2019. The infraorder Astacidea comprises five extant superfamilies, two of

(

Astacoidea Astacoidea is superfamily of freshwater crayfish that live in the Northern Hemisphere. The other superfamily of crayfish, Parastacoidea, lives in the Southern Hemisphere. Astacoidea consists of three families: Astacidae (from Europe and weste ...

and Parastacoidea), one of true

s (Nephropoidea), one of reef lobsters (the genus '' Enoplometopus''), and a number of fossil taxa. , the group contains 782 recognised species, over 400 of which are in the crayfish family Cambaridae. The members of the infraorder

Glypheidea Glypheidea is an infraorder of lobster-like decapod crustaceans, comprising a number of fossil forms and the two extant (living) genera ''Neoglyphea'' and '' Laurentaeglyphea'': The infraorder was thought to be extinct until a living species, ' ...

(containing numerous fossils and the two extant species '' Neoglyphea inopinata'' and '' Laurentaeglyphea neocaledonica'') were formerly included here. The

below shows Astacidea's internal relationships and the early split between

lobsters Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...

and

Taxonomy

* Palaeopalaemonoidea † *# Palaeopalaemonidae † * Enoplometopoidea *# Enoplometopidae *# Uncinidae † * Nephropoidea *# Chilenophoberidae † *#

Nephropidae Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...

*# Protastacidae † *# Stenochiridae † *

Astacidae Astacidae is a family of freshwater crayfish native to Europe and western North America. The family is made up of four extant (living) genera: The genera '' Astacus'' (which includes the European crayfish), ''Pontastacus'' (which includes the T ...

*# Cambaridae *# Cambaroididae *# Cricoidoscelosidae † * Parastacoidea *#

Parastacidae The Parastacidae are the family of freshwater crayfish found in the Southern Hemisphere. The family is a classic Gondwana-distributed taxon, with extant members in South America, Madagascar, Australia, New Zealand, and New Guinea, and extinct ...

References

{{Authority control Decapods Arthropod infraorders Taxa named by Pierre André Latreille