The marsupium or brood pouch, is a characteristic feature of Peracarida

Peracarida

The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or marsupium, formed from thin flattened plates borne on the basalmost segments of the legs Other...

, including the orders 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...

, 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...

 and Cumacea

Cumacea

Cumacea is an order of small marine crustaceans, occasionally called hooded shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans.-Anatomy:...

. It is an egg chamber formed by oostegites, which are appendices which are attached to the coxae (first segment) of the first pereiopods. Females lay their eggs directly into the brood chamber, and the young will develop there, undergoing several moult

Moult

In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...

s before emerging as miniature adults referred to as mancae. Males have no marsupium.