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]

Temporal range: Norian–Recent
Dardanus megistos2.jpg
The hermit crab Dardanus megistos
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
(unranked): Reptantia
Infraorder: Anomura
Macleay, 1838


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]


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]


Dendrobranchiata (prawns)  


Stenopodidea (boxer shrimp)  


Caridea (true shrimp)  

Reptantia (crawling/walking decapods)

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)  

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]


Porcellanidae (porcelain crabs)

Munididae (squat lobsters)

Parapaguridae (deep water sea anemone hermit crabs)

Eumunididae (squat lobster-like)

Hippidae (mole crabs or sand crabs)


Lithodidae (king crabs)

Paguridae (hermit crabs)

Diogenidae (left-handed hermit crabs)

Coenobitidae (terrestrial hermit crabs)


The infraorder Anomura contained seven extant superfamilies:[7][8][9][10]

Superfamily Members Families Photo
Aegloidea Aegla Aeglidae  
Aegla sp.
Chirostyloidea squat lobsters Chirostylidae
Eumunida picta
Eocarcinoidea Eocarcinus
Galatheoidea squat lobsters
porcelain crabs
Munidopsis serricornis
Hippoidea mole crabs
or sand crabs
Blepharipoda occidentalis
Lithodoidea king crabs Hapalogastridae
Lithodes santolla
Lomisoidea hairy stone crab Lomisidae
Paguroidea hermit crabs
coconut crab
Coenobita clypeatus

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


  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 (eds.). Decapod Crustacean Phylogenetics. Crustacean issues. 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.
  6. ^ a b Wolfe, Joanna M.; Breinholt, Jesse W.; Crandall, Keith A.; Lemmon, Alan R.; Lemmon, Emily Moriarty; Timm, Laura E.; Siddall, Mark E.; Bracken-Grissom, Heather D. (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. ^ 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.
  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.

External linksEdit

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