GILL or BRANCHIA, the name given to any structure specially adapted for aquatic respiration. Gills are found in some Annelida; most Mollusca; Crustacea; the aquatic Arachnida, such as the king-crab ; the larvae of many aquatic insects ; and in protochordates, fishes and most larval and a few adult Amphibia. In the Lamellibranchia (q.v.) among the molluscs and in Amphi oxus and the Tunicata (qq.v.), the gills are modified for feeding purposes, and in one group of lamellibranchs, the Septibranchia, they have entirely lost their respiratory function. (See MOLLUSCA,