Eumalacostraca

Eumalacostraca is a subclass of crustaceans, containing almost all living malacostracans, or about 40,000 described species. The remaining subclasses are the Phyllocarida and possibly the Hoplocarida. Eumalacostracans have 19 segments (5 cephalic, 8 thoracic and 6 abdominal). This arrangement is known as the 'caridoid facies', a term coined by William Thomas Calman in 1909. The thoracic limbs are jointed and used for swimming or walking. The common ancestor is thought to have had a carapace, and most living species possess one, but it has been lost in some subgroups. Calman identified the following features as distinguishing eumalacostracan crustaceans: Martin and Davis present the following classification of living eumalacostracans into orders, to which extinct orders have been added, indicated by †. The group as originally described by Karl Grobben included the Stomatopoda (mantis shrimp), and some modern experts continue to use this definition. This article follows Martin and Davis in excluding them; they are placed in their own subclass, Hoplocarida. Subclass Eumalacostraca Grobben, 1892