The first malacostracans appeared in the Cambrian period.

They feed on mollusks and crustaceans, particularly malacostracans.

The Eumalacostraca are a subclass of crustaceans, containing almost all living malacostracans, about 40,000 described species.

To bring in food particles, they make water currents with the thoracic appendages like the branchiopods and the malacostracans.

Martin and Davis present the following classification of living malacostracans into orders, to which extinct orders have been added, indicated by an obelisk (-).

They are ectoparasites that inhabit other crustaceans, namely ostracods, copepods, barnacles and malacostracans.

Malacostracans are sometimes contrasted with entomostracans, a name applied to all crustaceans outside the Malacostraca, and named after the obsolete taxon Entomostraca.