The Astacidea are distinguished from most other decapods by the presence of chelae (claws) on each of the first three pairs of pereiopods (walking legs), the first of which is much larger than the remaining two pairs.[1] The last two pairs of pereiopods are simple (without claws), except in Thaumastocheles, where the fifth pereiopod may have "a minute pincer".[2]
Distribution
Members of the infraorder Astacidea are found throughout the world – both in the oceans and in fresh water – except for mainland Africa and parts of Asia.[3]
Classification
Astacidea belongs to the group Reptantia, which consists of the walking/crawling decapods (lobsters and crabs).[4] Astacidea is the sister clade to the infraorder Polychelida, a small group of crustaceans restricted to deep waters. The cladogram below shows Astacidea's placement within the larger orderDecapoda, from analysis by Wolfe et al., 2019.[5]
^Heather D. Bracken-Grissom; Shane T. Ahyong; Richard D. Wilkinson; Rodney M. Feldmann; Carrie E. Schweitzer; Jesse W. Breinholt; Matthew Bendall; Ferran Palero; Tin-Yam Chan; Darryl L. Felder; Rafael Robles; Ka-Hou Chu; Ling-Ming Tsang; Dohyup Kim; Joel W. Martin; Keith A. Crandall (July 2014). "The Emergence of Lobsters: Phylogenetic Relationships, Morphological Evolution and Divergence Time Comparisons of an Ancient Group (Decapoda: Achelata, Astacidea, Glypheidea, Polychelida)". Systematic Biology. 63 (4): 457–479. doi:10.1093/sysbio/syu008. PMID24562813.