Arthrostraca was a subdivision of Malacostraca

Malacostraca

Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...

 which comprised Crustacea in which the first, sometimes the second, thoracic segment is fused with the head and bears maxillipedes; the remaining seven being free and bearing legs. The eyes of members of this group were usually sessile. The group was in turn divided into the Amphipoda

Amphipoda

Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...

 and Isopoda

Isopoda

Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...

. Common examples of members of this former subdivision are the pill bug and the woodlouse

Woodlouse

A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs...

.