Ionotropic Receptors (IR) are a variant subfamily of ionotropic glutamate receptors which lack conserved glutamate-interacting residues. They are largely thought to function as ligand-gated ion channels involved in chemosensation. IRs were first described in Drosophila in 2009 and are found throughout the protostome lineage. They can been dived into two subgroups: (1) antennal - olfactory receptors expressed in the antenna and, (2) divergent - largely species-specific, with low amino acid sequence identity. Expressed in gustatory organs, they are believed to be taste receptors. (Adapted from FBrf0211681 and FBrf0222310).