Either of a pair of ducts (coelomoducts) found in the third segment of a crustacean and opening to the exterior at the base of the second antenna. They function as osmoregulatory organs. For example, in the antennal gland of the freshwater crayfish (Astacus), fluid is filtered from the blood into an end sac and passes through a tubular labyrinth, where ions are reabsorbed, to produce a hypotonic urine that passes via a renal tubule to the bladder.