Anomura

Anomura; Temporal range: Late Triassic: Norian - Recent, 227–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	The hermit crab Dardanus megistos
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Clade:	Pancrustacea
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Clade:	Reptantia
Infraorder:	Anomura; Macleay, 1838
Superfamilies
	Aegloidea; Chirostyloidea; † Eocarcinoidea; Galatheoidea; Hippoidea; Lomisoidea; Paguroidea;

Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Several groups such as the king crabs and porcelain crabs within the Anomura have independently undergone carcinisation, acquiring the armoured crab body plan with a concealed tail. It is the sister group to the "true crabs" or Brachyura.^[2]

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 and slipper lobsters)

	Polychelida (benthic crustaceans)

	Glypheidea (glypheoid lobsters)

	Astacidea (lobsters and crayfish)

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

Gebiidea (mud lobsters and mud shrimp)

	Anomura (hermit crabs and allies)

	Brachyura ("true" crabs)

(crawling /
walking
decapods)

Some of the internal relationships within Anomura are shown in the 2026 cladogram found below.^[8]

Brachyura ("true" crabs)

Anomura

Galatheoidea

Porcellanidae (porcelain crabs)

Munidopsidae (squat lobsters)

	Galatheidae (squat lobsters)

	Munididae (squat lobsters)

Pagurus longicarpus

	Lithodidae (king crabs)

	Paguridae

Pylochelidae (symetrical hermit crabs)

Lomisidae (hairy stone crabs)

Aeglidae (pancoras)

Chirostyloidea

	Kiwaidae (yeti crabs)

	Sternostylidae

Hippoidea

Blepharipodidae (mole crabs)

	Albuneidae (mole crabs)

	Hippidae (mole crabs)

Paguroidea

	Diogenidae (left-handed hermit crabs)

	Coenobitidae (terrestrial hermit crabs)

Classification

The infraorder Anomura contained seven extant superfamilies:^[9]^[10]^[11]^[12]

Superfamily	Members	Families	Photo
Aegloidea	pancoras	Aeglidae	Aegla sp.
Chirostyloidea	squat lobsters	Chirostylidae Eumunididae Kiwaidae Sternostylidae	Eumunida picta
† Eocarcinoidea	† Eocarcinus † Platykotta	† Eocarcinidae † Platykottidae
Galatheoidea	squat lobsters porcelain crabs	Galatheidae Munididae Munidopsidae Porcellanidae † Retrorsichelidae	Munidopsis serricornis (Munidopsidae)
Hippoidea	mole crabs	Albuneidae Blepharipodidae Hippidae	Blepharipoda occidentalis (Blepharipodidae)
Lomisoidea	hairy stone crab	Lomisidae	Lomis hirta
Paguroidea	hermit crabs coconut crab	Coenobitidae Diogenidae Lithodidae Paguridae Parapaguridae Probeebeidae Pylochelidae Pylojacquesidae Xylopaguridae	Coenobita clypeatus (Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian (Late Triassic) Period in the United Arab Emirates.^[10]

References

1 2 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. S2CID 5612385.
↑ Scholtz, Gerhard; Richter, Stefan (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.
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.
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. ISBN 978-1-4200-9258-5.
↑ 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. Bibcode:2011ZooAn.250..343K. doi:10.1016/j.jcz.2011.04.004.
↑ 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. Bibcode:2001JPal...75..330S. doi:10.1666/0022-3360(2001)075<0330:DOTFHM>2.0.CO;2. S2CID 85997166.
↑ 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.
↑ Hwang, Hee-seung; Jung, Jibom (2026-01-12). "Comparative phylomitogenomic analyses provide insights into adaptation and carcinization in Anomura". Animal Cells and Systems. 30 (1): 83–103. doi:10.1080/19768354.2025.2607863. ISSN 1976-8354.
↑ 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.
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 (1): 93–102. Bibcode:2011PalZ...85...93C. doi:10.1007/s12542-010-0080-y. S2CID 5612385.
↑ 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. Bibcode:2011MolPE..58..157S. doi:10.1016/j.ympev.2010.11.011. PMID 21095236.
↑ WoRMS (2018). "Anomura". WoRMS. World Register of Marine Species. Retrieved 2018-09-28.

External links

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

[Jerome2011-1] 1 2 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. S2CID 5612385.

[2] Scholtz, Gerhard; Richter, Stefan (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.

[Poore-3] 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.

[Ahyong-4] 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. ISBN 978-1-4200-9258-5.

[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. Bibcode:2011ZooAn.250..343K. doi:10.1016/j.jcz.2011.04.004.

[S&F-6] 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. Bibcode:2001JPal...75..330S. doi:10.1666/0022-3360(2001)075<0330:DOTFHM>2.0.CO;2. S2CID 85997166.

[Wolfe2019-7] 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.

[8] Hwang, Hee-seung; Jung, Jibom (2026-01-12). "Comparative phylomitogenomic analyses provide insights into adaptation and carcinization in Anomura". Animal Cells and Systems. 30 (1): 83–103. doi:10.1080/19768354.2025.2607863. ISSN 1976-8354.

[Grave-9] 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.

[Chablais-10] 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 (1): 93–102. Bibcode:2011PalZ...85...93C. doi:10.1007/s12542-010-0080-y. S2CID 5612385.

[Schnabel-11] 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. Bibcode:2011MolPE..58..157S. doi:10.1016/j.ympev.2010.11.011. PMID 21095236.

[12] WoRMS (2018). "Anomura". WoRMS. World Register of Marine Species. Retrieved 2018-09-28.

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Anomura

Description

Evolution

Classification

References

External links