14-617: 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 ). 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
28-625: Is Platykotta , from the Norian – Rhaetian (Late Triassic) Period in the United Arab Emirates . [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Decapod Dendrobranchiata Pleocyemata See text for superfamilies. The Decapoda or decapods ( lit. ' ten-footed ' ) are an order of crustaceans within the class Malacostraca , and includes crabs , lobsters , crayfish , shrimp , and prawns . Most decapods are scavengers . The order
42-521: Is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3,000 species) and Anomura including hermit crabs , porcelain crabs , squat lobsters (about 2500 species) making up the bulk of the remainder. The earliest fossils of the group date to the Devonian . Decapods can have as many as 38 appendages, arranged in one pair per body segment. As
56-504: Is wide acceptance from morphological and molecular data that Anomura and Brachyura ("true" crabs) are sister taxa , together making up the clade Meiura. 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 . The cladogram below shows Anomura's placement within
70-501: The "white shrimp", Litopenaeus setiferus . The Pleocyemata include the remaining groups, including "true shrimp". Those groups that usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia. This classification to the level of superfamilies follows De Grave et al. Order Decapoda Latreille, 1802 [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Parapaguridae The Parapaguridae are
84-537: The abdomen. They are called pleopods . There is one final pair called uropods , which, with the telson , form the tail fan. A 2019 molecular clock analysis suggested decapods originated in the Late Ordovician around 455 million years ago, with the Dendrobranchiata (prawns) being the first group to diverge. The remaining group, called Pleocyemata , then diverged between the swimming shrimp groupings and
98-533: The cladogram above, the clade Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the sister clade to Polychelida , within Reptantia . Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata . The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as
112-535: The crawling/walking group called Reptantia , consisting of lobsters and crabs . High species diversification can be traced to the Jurassic and Cretaceous periods, which coincides with the rise and spread of modern coral reefs , a key habitat for the decapods. Despite the inferred early origin, the oldest fossils of the group such as Palaeopalaemon only date to the Late Devonian . The cladogram below shows
126-631: The internal relationships of Decapoda, from analysis by Wolfe et al. (2019). Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] In
140-827: The internal relationships within Anomura are shown in the cladogram below, which shows Hippidae as sister to Paguroidea, and resolves Parapaguridae outside of Paguroidea: Brachyura ("true" crabs) [REDACTED] Porcellanidae (porcelain crabs) [REDACTED] Munididae (squat lobsters) [REDACTED] Parapaguridae (deep water sea anemone hermit crabs) [REDACTED] Eumunididae (squat lobster-like) [REDACTED] Hippidae (mole crabs or sand crabs) [REDACTED] Lithodidae (king crabs) [REDACTED] Paguridae (hermit crabs) [REDACTED] Diogenidae (left-handed hermit crabs) [REDACTED] Coenobitidae (terrestrial hermit crabs) [REDACTED] The infraorder Anomura contained seven extant superfamilies: The oldest fossil attributed to Anomura
154-633: The larger order Decapoda , from analysis by Wolfe et al. (2019). Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] Some of
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#1732858913414168-450: 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. Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae ), a "crab" with only eight visible pereiopods is generally an anomuran. The infraorder Anomura belongs to the group Reptantia , which consists of the walking/crawling decapods ( lobsters and crabs). There
182-630: The name Decapoda (from the Greek δέκα , deca- , "ten", and πούς / ποδός , -pod , "foot") implies, ten of these appendages are considered legs. They are the pereiopods , found on the last five thoracic segments. In many decapods, one pair of these "legs" has enlarged pincers, called chelae , with the legs being called chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts , antennae, and antennules. There are five more pairs of appendages on
196-487: The unusual variety of forms in this group; whereas all crabs share some obvious similarities, the various groups of anomurans are quite dissimilar. The group has been moulded by several instances of carcinisation – the development of a crab-like body form. Thus, the king crabs (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation. As decapods (meaning ten-legged ), anomurans have ten pereiopods , but
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