The Achelata is an infra-order of the decapod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s, holding the

spiny lobster Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...

slipper lobster Slipper lobsters are a family (Scyllaridae) of about 90 species of achelate crustaceans, in the Decapoda clade Reptantia, found in all warm oceans and seas. They are not true lobsters, but are more closely related to spiny lobsters and furry lo ...

s and their fossil relatives.

Description

The name "Achelata" derives from the fact that all the members of this group lack the

chelae A chela ()also called a claw, nipper, or pinceris a pincer (biology), pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are ...

(claws) that are found on almost all other decapods (from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

, = "not", , = "claw"). They are further united by the great enlargement of the second antennae, by the special "

phyllosoma The phyllosoma is the larval stage of spiny, slipper and coral lobsters (Palinuridae, Scyllaridae and Synaxidae), and represents one of the most significant characteristics that unify them into the taxon Achelata. Its body is remarkably thin ...

" form of the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

, and by a number of other characters. Larva de phyllosoma

Classification and fossil record

The

infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Achelata belongs to the group

Reptantia Reptantia is a clade of decapod crustaceans named in 1880 which includes lobsters, crabs and many other well-known crustaceans. Classification In older classifications, Reptantia was one of the two sub-orders of Decapoda alongside Natantia, wi ...

, which consists of the walking/crawling decapods (lobsters and

crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

). The cladogram below shows Achelata's placement within the larger order

Decapoda The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is esti ...

, from analysis by Wolfe ''et al.'', 2019. Achelata contains the

s (Palinuridae), the

s (Scyllaridae) and the

furry lobster Furry lobsters (sometimes called coral lobsters) are small decapod crustaceans, closely related to the slipper lobsters and spiny lobsters. The antennae are not as enlarged as in spiny and slipper lobsters, and the body is covered in short hai ...

s (Synaxidae, now usually included in Palinuridae), as well as two extinct families, Cancrinidae and Tricarinidae. Both Palinuridae and Scyllaridae have a

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

extending back to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

. The two fossil families contain a single genus each; '' Tricarina'' is known from a single Cretaceous fossil, while '' Cancrinos'' is known from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

and Cretaceous. One estimate of the divergence between Achelata and its closest relatives places it at about .

References

External links

* {{Taxonbar, from=Q1191353 Arthropod infraorders Extant Late Jurassic first appearances