Shrimp
Decapods

There is little agreement among taxonomists concerning the phylogeny of crustaceans. Within the decapods, "every study gives totally different results. Nor do even one of these studies match any of the rival morphology studies". Some taxonomists identify shrimp with the infraorder Caridea and prawns with the suborder Dendrobranchiata. While different experts give different answers, there is no disagreement that the caridean species are shrimp. There are over 3000 caridean species. Occasionally they are referred to as "true shrimp".

Traditionally, decapods were divided into two suborders: the Natantia (or swimmers) and the Reptantia (or walkers). The Natantia or swimmers included the shrimp. They were defined by their abdomen which, together with its appendages was well adapted for swimming. The Reptantia or walkers included the crabs and lobsters. These species have small abdominal appendages, but robust legs well adapted for walking. The Natantia was thought to be paraphyletic; that is, it was thought that originally all decapods were like shrimp.

However, classifications are now based on clades, and the paraphyletic suborder Natantia has been discontinued. "On this basis, taxonomic classifications now divide the order Decapoda into the two suborders: Dendrobranchiata for the largest shrimp clade, and Pleocyemata for all other decapods. The Pleocyemata are in turn divided into half a dozen infra-orders"

Other decapod crustaceans also called shrimp, are the ghost or mud shrimp belonging to the infra-order Thalassinidea. In Australia they are called yabbies. The monophyly of the group is not certain; recent studies have suggested dividing the group into two infraorders, Gebiidea and Axiidea.
detectable_format:number_bullet_lists[2], change_case:english_lowercase