The name "Achelata" derives from the fact that all the members of this group lack the chelae (claws) that are found on almost all other decapods (from the Ancient Greekἀ-, a- = "not", χηλή, chela = "claw"). They are further united by the great enlargement of the second antennae, by the special "phyllosoma" form of the larva, and by a number of other characters.[2]
Classification and fossil record
The infraorder Achelata belongs to the group Reptantia, which consists of the walking/crawling decapods (lobsters and crabs). The cladogram below shows Achelata's placement within the larger orderDecapoda, from analysis by Wolfe et al., 2019.[3]
Both Palinuridae and Scyllaridae have a fossil record extending back to the Cretaceous.[5][6] The two fossil families contain a single genus each;[1]Tricarina is known from a single Cretaceous fossil,[7] while Cancrinos is known from the Jurassic and Cretaceous.[6] One estimate of the divergence between Achelata and its closest relatives places it at about 341 million years ago.[8]