Decapoda

The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, including crabs, lobsters, crayfish, shrimp, and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species.[1] Nearly half of these species are crabs, with the shrimp (about 3,000 species) and Anomura including hermit crabs, porcelain crabs, squat lobsters (about 2500 species) making up the bulk of the remainder.[1] The earliest fossils of the group date to the Devonian.

For other uses of "decapod", see Decapod (disambiguation).
Not to be confused with Decapodiformes.

Decapoda
Temporal range:
From left to right: Grapsus grapsus (Brachyura), Coconut crab (Anomura), Lysmata amboinensis (Caridea), Homarus gammarus (Astacidea).
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Superorder: Eucarida
Order: Decapoda
Latreille, 1802
Suborders

Dendrobranchiata
Pleocyemata
See text for superfamilies.

Anatomy
Main article: Decapod anatomy

Decapods can have as many as 38 appendages,[2] arranged in one pair per body segment. As the name Decapoda (from the Greek δέκα, deca-, "ten", and πούς / ποδός, -pod, "foot") implies, ten of these appendages are considered legs. They are the pereiopods, found on the last five thoracic segments.[2] In many decapods, one pair of these "legs" has enlarged pincers, called chelae, with the legs being called chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts, antennae, and antennules. There are five more pairs of appendages on the abdomen. They are called pleopods. There is one final pair called uropods, which, with the telson, form the tail fan.[2]

"Decapoda" from Ernst Haeckel's Kunstformen der Natur, 1904

Evolution

A 2019 molecular clock analysis suggested decapods originated in the Late Ordovician around 455 million years ago, with the Dendrobranchiata (prawns) being the first group to diverge. The remaining group, called Pleocyemata, then diverged between the swimming shrimp groupings and the crawling/walking group called Reptantia, consisting of lobsters and crabs. High species diversification can be traced to the Jurassic and Cretaceous periods, which coincides with the rise and spread of modern coral reefs, a key habitat for the decapods.[3] Despite the inferred early origin, the oldest fossils of the group such as Palaeopalaemon only date to the Late Devonian.[4]

The cladogram below shows the internal relationships of Decapoda, from analysis by Wolfe et al. (2019).[3]

 Decapoda 
                

Dendrobranchiata (prawns)

 Pleocyemata 

Stenopodidea (boxer shrimp)

Procarididea

Caridea (true shrimp)

 Reptantia 

Achelata (spiny lobsters, slipper lobsters)

Polychelida (benthic crustaceans)

Astacidea (lobsters, crayfish)

Axiidea (mud shrimp, ghost shrimp, or burrowing shrimp)

Gebiidea (mud lobsters and mud shrimp)

Anomura (hermit crabs and others)

Brachyura (crabs)

 (crawling / walking decapods) 

In the cladogram above, the clade Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the sister clade to Polychelida, within Reptantia.[3]

Classification

Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata. The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as the "white shrimp", Litopenaeus setiferus. The Pleocyemata include the remaining groups, including "true shrimp".[5] Those groups that usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia.[6]

This classification to the level of superfamilies follows De Grave et al.[1]

Whiteleg shrimp, Litopenaeus vannamei (Dendrobranchiata: Penaeoidea)
Heterocarpus ensifer (Caridea: Pandaloidea)
Austropotamobius pallipes (Astacidea: Astacoidea)
Upogebia deltaura (Gebiidea: Upogebiidae)
California spiny lobster, Panulirus interruptus (Achelata: Palinuridae)
Polycheles sculptus (Polychelida: Polychelidae)
Australian land hermit crab, Coenobita variabilis (Anomura: Paguroidea)
Atlantic blue crab, Callinectes sapidus (Brachyura: Portunoidea)

Order Decapoda Latreille, 1802

See also

References
  1. Sammy De Grave; N. Dean Pentcheff; Shane T. Ahyong; et al. (2009). "A classification of living and fossil genera of decapod crustaceans" (PDF). Raffles Bulletin of Zoology. Suppl. 21: 1–109. Archived from the original (PDF) on 2011-06-06.
  2. "Decapoda characters and anatomy". University of Bristol: Decapoda characters. Archived from the original on 10 November 2013. Retrieved 11 December 2017.
  3. Wolfe, Joanna M.; Breinholt, Jesse W.; Crandall, Keith A.; Lemmon, Alan R.; Lemmon, Emily Moriarty; Timm, Laura E.; et al. (24 April 2019). "A phylogenomic framework, evolutionary timeline, and genomic resources for comparative studies of decapod crustaceans". Proceedings of the Royal Society B. 286 (1901). doi:10.1098/rspb.2019.0079. PMC 6501934. PMID 31014217.
  4. Gueriau, Pierre; Rak, Štěpán; Broda, Krzysztof; Kumpan, Tomáš; Viktorýn, Tomáš; Valach, Petr; Zatoń, Michał; Charbonnier, Sylvain; Luque, Javier (2020-10-25). "Exceptional Late Devonian arthropods document the origin of decapod crustaceans". doi:10.1101/2020.10.23.352971. S2CID 226229304. {{cite journal}}: Cite journal requires |journal= (help)
  5. Elena Mente (2008). Reproductive Biology of Crustaceans: Case Studies of Decapod Crustaceans. Science Publishers. p. 16. ISBN 978-1-57808-529-3.
  6. G. Scholtz; S. Richter (1995). "Phylogenetic systematics of the reptantian Decapoda (Crustacea, Malacostraca)". Zoological Journal of the Linnean Society. 113 (3): 289–328. doi:10.1006/zjls.1995.0011.
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