Significance In mammals, AMPA-type glutamate receptors (GluAs) are expressed ubiquitously in the central nervous system and play critical roles in synaptic plasticity, learning, and memory. Here we examined GluAs in the ascidian, Ciona intestinalis , and determined that they are expressed in a limited subset of cells during early development. We further find that GluAs are required for development of the ocellus, a photoreceptive organ used during the swimming stage, and for tail resorption and body axis rotation during metamorphosis. These functions require ion influx through GluAs. This is a demonstration of an in vivo requirement for GluAs in organ formation and morphogenesis. GluAs are also expressed during mammalian development, suggesting that developmental roles of GluAs may be functionally conserved.