Anomura

Short description: Infraorder of crustaceans

Anomura

Temporal range: Late Triassic: Norian - Recent, 227–0 Ma[1]

PreЄ

The hermit crab Dardanus megistos
Scientific classification
Kingdom:  | Animalia
Phylum:  | Arthropoda
Class:  | Malacostraca
Order:  | Decapoda
Suborder:  | Pleocyemata
(unranked):  | Reptantia
Infraorder:  | Anomura
Macleay, 1838
Superfamilies

* Aegloidea
* Chirostyloidea
* † Eocarcinoidea
* Galatheoidea
* Hippoidea
* Lithodoidea
* Lomisoidea
* Paguroidea

Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word crab, all true crabs are in the sister group to the Anomura, the Brachyura (the two groups together form the clade Meiura).[2]

## Contents

* 1 Description
* 2 Evolution
* 3 Classification
* 4 References
* 5 External links

## Description

The name Anomura derives from an old classification in which reptant decapods were divided into Macrura (long-tailed), Brachyura (short-tailed) and Anomura (differently-tailed). The alternative name Anomala reflects the unusual variety of forms in this group; whereas all crabs share some obvious similarities, the various groups of anomurans are quite dissimilar.[3]

The group has been moulded by several instances of carcinisation – the development of a crab-like body form.[4] Thus, the king crabs (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation.[4]

As decapods (meaning ten-legged), anomurans have ten pereiopods, but the last pair of these is reduced in size, and often hidden inside the gill chamber (under the carapace) to be used for cleaning the gills.[5][3] Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae),[6] a "crab" with only eight visible pereiopods is generally an anomuran.[3]

## Evolution

The infraorder Anomura belongs to the group Reptantia, which consists of the walking/crawling decapods (lobsters and crabs). There is wide acceptance from morphological and molecular data that Anomura and Brachyura (true crabs) are sister taxa, together making up the clade Meiura.[4] Anomura likely diverged from Brachyura in the Late Triassic period, with the earliest discovered Anomuran fossil Platykotta akaina dating from the Norian–Rhaetian aged Ghalilah Formation of the United Arab Emirates.[1]

The cladogram below shows Anomura's placement within the larger order Decapoda, from analysis by Wolfe et al. (2019).[7]

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)

|

Meiura |  |  |

Anomura (hermit crabs and others)

|

Brachyura (crabs)

(crawling / walking decapods)

Some of the internal relationships within Anomura can be shown in the cladogram below, which shows Hippidae as sister to Paguroidea, and resolves Parapaguridae outside of Paguroidea:[7]

Anomura |  |  |  |  |

Porcellanidae (porcelain crabs)

|

Munididae (squat lobsters)

|  |  |  |  |

Parapaguridae (deep water sea anemone hermit crabs)

|

Eumunididae (squat lobster-like)

|  |  |

Hippidae (mole crabs or sand crabs)

|

Paguroidea |  |  |  |  |

Lithodidae (king crabs)

|

Paguridae (hermit crabs)

|  |  |

Diogenidae (left-handed hermit crabs)

|

Coenobitidae (terrestrial hermit crabs)

## Classification

The infraorder Anomura contained seven extant superfamilies:[8][9][10][11]

Superfamily | Members | Families | Photo

|
|
|

Aegloidea | Aegla | Aeglidae |
Aegla sp.
Chirostyloidea | squat lobsters | Chirostylidae
Eumunididae
Kiwaidae |
Eumunida picta
† Eocarcinoidea | † Eocarcinus
† Platykotta | † Eocarcinidae
† Platykottidae |
Galatheoidea | squat lobsters
porcelain crabs | Galatheidae
Munididae
Munidopsidae
Porcellanidae
† Retrorsichelidae |
Munidopsis serricornis
(Munidopsidae)
Hippoidea | mole crabs
or sand crabs | Albuneidae
Blepharipodidae
Hippidae |
Blepharipoda occidentalis
(Blepharipodidae)
Lithodoidea | king crabs | Hapalogastridae
Lithodidae |
Lithodes santolla
(Lithodidae)
Lomisoidea | hairy stone crab | Lomisidae |
Lomis hirta
(Lomisidae)
Paguroidea | hermit crabs
coconut crab | Coenobitidae
Diogenidae
Paguridae
Parapaguridae
Parapylochelidae
Pylochelidae
Pylojacquesidae | Error creating thumbnail: Unable to save thumbnail to destination
Coenobita clypeatus
(Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian (Late Triassic) Period in the United Arab Emirates.[9]

## References

1. ↑ 1.0 1.1 Chablais, Jérôme; Feldmann, Rodney M.; Schweitzer, Carrie E. (11 August 2010). "A new Triassic decapod, Platykotta akaina, from the Arabian shelf of the northern United Arab Emirates: earliest occurrence of the Anomura". Paläontol Z 85 (2011): 93-102. doi:10.1007/s12542-010-0080-y. https://link.springer.com/article/10.1007/s12542-010-0080-y.
2. ↑ Gerhard Scholtz; Stefan Richter (1995). "Phylogenetic systematics of the reptantian Decapoda (Crustacea, Malacostraca)". Zoological Journal of the Linnean Society 113 (3): 289–328. doi:10.1111/j.1096-3642.1995.tb00936.x. http://arthroinfo.org/pdfs/826/826.pdf.
3. ↑ 3.0 3.1 3.2 Gary Poore (2004). "Anomura – hermit crabs, porcelain crabs and squat lobsters". Marine Decapod Crustacea of Southern Australia: a Guide to Identification. CSIRO Publishing. pp. 215–287. ISBN 978-0-643-09925-8. https://books.google.com/books?id=TptuZCY3OU0C&pg=PA215.
4. ↑ 4.0 4.1 4.2 Shane T. Ahyong; Kareen E. Schnabel; Elizabeth W. Maas (2009). "Anomuran phylogeny: new insights from molecular data". Decapod Crustacean Phylogenetics. Crustacean issues. 18. CRC Press. pp. 399–414. doi:10.1201/9781420092592-c20. ISBN 978-1-4200-9258-5. https://books.google.com/books?id=Bxs6SgSW2kQC&pg=PA399.
5. ↑ Jonas Keiler; Stefan Richter (2011). "Morphological diversity of setae on the grooming legs in Anomala (Decapoda: Reptantia) revealed by scanning electron microscopy". Zoologischer Anzeiger 250 (4): 343–366. doi:10.1016/j.jcz.2011.04.004.
6. ↑ Carrie E. Schweitzer; Rodney M. Feldmann (2001). "Differentiation of the fossil Hexapodidae Miers, 1886 (Decapoda: Brachyura) from similar forms". Journal of Paleontology 75 (2): 330–345. doi:10.1666/0022-3360(2001)075<0330:DOTFHM>2.0.CO;2. http://decapoda.nhm.org/pdfs/10789/10789.pdf.
7. ↑ 7.0 7.1 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. PMID 31014217.
8. ↑ Sammy De Grave et al. (2009). "A classification of living and fossil genera of decapod crustaceans". Raffles Bulletin of Zoology Suppl. 21: 1–109. https://decapoda.nhm.org/pdfs/31051/31051.pdf.
9. ↑ 9.0 9.1 Jérôme Chablais; Rodney M. Feldmann; Carrie E. Schweitzer (2011). "A new Triassic decapod, Platykotta akaina, from the Arabian shelf of the northern United Arab Emirates: earliest occurrence of the Anomura". Paläontologische Zeitschrift 85: 93–102. doi:10.1007/s12542-010-0080-y. http://decapoda.nhm.org/pdfs/31744/31744.pdf.
10. ↑ K. E. Schnabel; S. T. Ahyong; E. W. Maas (2011). "Galatheoidea are not monophyletic – molecular and morphological phylogeny of the squat lobsters (Decapoda: Anomura) with recognition of a new superfamily". Molecular Phylogenetics and Evolution 58 (2): 157–168. doi:10.1016/j.ympev.2010.11.011. PMID 21095236.
11. ↑ WoRMS (2018). "Anomura". WoRMS. World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=106671.

## External links

Wikidata ☰ Q526867 entry

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