any of an order (Mysidacea) of small, shrimplike, malacostracan crustaceans with a carapace over most of the thorax
See mysid in American Heritage Dictionary 4
(mīˈsĭd)
noun
Any of various small, shrimplike, chiefly marine crustaceans of the order Mysidacea, the females of which carry their eggs in a pouch beneath the thorax. Also called opossum shrimp.