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 Greek ἀ-, 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] 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 order Decapoda, from analysis by Wolfe et al., 2019.

[6] One estimate of the divergence between Achelata and its closest relatives places it at about 341 million years ago.