We describe the cloning and analysis of genomic and cDNA copies of a gene from sea anemones that encodes a new member of the G-protein-coupled receptor family. The receptor shows similarity to previously described receptors for biogenic amines such as adrenaline, serotonin, and octopamine, as well as a variety of small molecule agonists and peptides, although we have been unable to determine which ligand is the natural agonist. Antibodies generated against the recombinant receptor protein identify a single protein with a molecular weight of 66 kDa in membrane preparations. Immunofluorescence studies using the same antibody have enabled localization of the receptor in the nervous system. Western blotting and RT-PCR analysis reveal that a homologue of this receptor is expressed in jellyfish and soft coral. We suggest that the receptor plays a role in neurotransmission in the sea anemone and other members of the phylum Cnidaria.