Anomura

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Anomura
Temporal range: Norian–Recent
Dardanus megistos2.jpg
The hermit crab Dardanus megistos
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
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 includes 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[edit]

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

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]

Classification[edit]

The infraorder Anomura is divided into nine superfamilies:[5][6][7]

Superfamily Members Families Photo
Aegloidea Aegla Aeglidae
Chirostyloidea squat lobsters Chirostylidae
Eumunididae
Kiwaidae
Eumunida picta.jpg
Eumunida picta
Eocarcinoidea Eocarcinus
Platykotta
Eocarcinidae
Platykottidae
Galatheoidea squat lobsters
porcelain crabs
Galatheidae
Munididae
Munidopsidae
Porcellanidae
Retrorsichelidae
Munidopsis tridentata.jpg
Munidopsis serricornis
(Munidopsidae)
Hippoidea mole crabs
or sand crabs
Albuneidae
Blepharipodidae
Hippidae
Blepharipoda.jpg
Blepharipoda occidentalis
(Blepharipodidae)
Lithodoidea king crabs Hapalogastridae
Lithodidae
Dessus.lithodes.santolla.JPG
Lithodes santolla
(Lithodidae)
Lomisoidea hairy stone crab Lomisidae
Paguroidea hermit crabs
coconut crab
Coenobitidae
Diogenidae
Paguridae
Parapaguridae
Parapylochelidae
Pylochelidae
Pylojacquesidae
Caribbean hermit crab.JPG
Coenobita clypeatus
(Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the NorianRhaetian of the United Arab Emirates.[6]

References[edit]

  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. ^ a b c 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. ^ a b c 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. Decapod Crustacean Phylogenetics. Crustacean issues 18. CRC Press. pp. 399–414. doi:10.1201/9781420092592-c20. ISBN 978-1-4200-9258-5. 
  4. ^ 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. 
  5. ^ Sammy De Grave, N. Dean Pentcheff, Shane T. Ahyong et al. (2009). "A classification of living and fossil genera of decapod crustaceans". Raffles Bulletin of Zoology. Suppl. 21: 1–109. 
  6. ^ a b 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. 
  7. ^ 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. 

External links[edit]

  • Media related to Anomura at Wikimedia Commons
  • Data related to Anomura at Wikispecies