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

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).[1]

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.[2]

The group has been moulded by several instances of carcinisation – the development of a crab-like body form.[3] Thus, the king crabs (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation.[3]

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.[4][2] Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae),[5] a "crab" with only eight visible pereiopods is generally an anomuran.[2]

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.[3] The cladogram below shows Anomura's placement within the larger order Decapoda, from analysis by Wolfe et al. (2019).[6]

 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:[6]

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:[7][8][9][10]

SuperfamilyMembersFamiliesPhoto
AegloideaAeglaAeglidae
Aegla sp.
Chirostyloideasquat lobstersChirostylidae
Eumunididae
Kiwaidae
Eumunida picta
† Eocarcinoidea† Eocarcinus
† Platykotta		† Eocarcinidae
† Platykottidae
Galatheoideasquat lobsters
porcelain crabs		Galatheidae
Munididae
Munidopsidae
Porcellanidae
† Retrorsichelidae
Munidopsis serricornis
(Munidopsidae)
Hippoideamole crabs
or sand crabs		Albuneidae
Blepharipodidae
Hippidae
Blepharipoda occidentalis
(Blepharipodidae)
Lithodoideaking crabsHapalogastridae
Lithodidae
Lithodes santolla
(Lithodidae)
Lomisoideahairy stone crabLomisidae
Lomis hirta
(Lomisidae)
Paguroideahermit crabs
coconut crab		Coenobitidae
Diogenidae
Paguridae
Parapaguridae
Parapylochelidae
Pylochelidae
Pylojacquesidae
Coenobita clypeatus
(Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian (Late Triassic) Period in the United Arab Emirates.[8]

References

  1. ↑ Gerhard Scholtz; Stefan Richter (1995). "Phylogenetic systematics of the reptantian Decapoda (Crustacea, Malacostraca)" (PDF). Zoological Journal of the Linnean Society. 113 (3): 289–328. doi:10.1111/j.1096-3642.1995.tb00936.x.
  2. 1 2 3 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.
  3. 1 2 3 Shane T. Ahyong; Kareen E. Schnabel; Elizabeth W. Maas (2009). "Anomuran phylogeny: new insights from molecular data". In Joel W. Martin; Keith A. Crandall; Darryl L. Felder (eds.). Decapod Crustacean Phylogenetics. Crustacean issues. Vol. 18. CRC Press. pp. 399–414. doi:10.1201/9781420092592-c20. ISBN 978-1-4200-9258-5.
  4. ↑ 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.
  5. ↑ Carrie E. Schweitzer; Rodney M. Feldmann (2001). "Differentiation of the fossil Hexapodidae Miers, 1886 (Decapoda: Brachyura) from similar forms" (PDF). Journal of Paleontology. 75 (2): 330–345. doi:10.1666/0022-3360(2001)075<0330:DOTFHM>2.0.CO;2. S2CID 85997166.
  6. 1 2 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.
  7. ↑ 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.
  8. 1 2 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" (PDF). Paläontologische Zeitschrift. 85: 93–102. doi:10.1007/s12542-010-0080-y. S2CID 5612385.
  9. ↑ 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.
  10. ↑ WoRMS (2018). "Anomura". WoRMS. World Register of Marine Species. Retrieved 2018-09-28.
  • Media related to Anomura at Wikimedia Commons
  • Data related to Anomura at Wikispecies
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