Numbers
~40,000 spp, worldwide, including approximately:
15,000 spp. in order Decapoda
10,000 spp. in order Isopoda
9,500 spp. in order Amphipoda
(1)Remarks
The largest class of Crustacea. The vast majority of species are marine but the class also includes many freshwater and terrestrial species. The freshwater fauna includes mostly members of Amphipoda, Isopoda, and Decapoda, while the terrestrial fauna is dominated by isopods, about 5,000 species of which are terrestrial.