thoracostraca

from The Century Dictionary.

• In some systems, a division of malacostracous crustaceans, including the podophthalmous or stalk-eyed crustaceans, as crabs, shrimps, prawns, and lobsters: nearly conterminous with Podophthalma.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (Zoöl.) An extensive division of Crustacea, having a dorsal shield or carapec� ��niting all, or nearly all, of the thoracic somites to the head. It includes the crabs, lobsters, shrimps, and similar species.