Table 1. The five classes of GPCRs in animal genomes and their representation in C. elegans.

Modified from [10].

Class 1	Subclass 1	Gene number in C. elegans
Rhodopsin (Class A)	chemosensory	1,341 a
	peptidergic	153 b
	aminergic	16
	muscarinic (acetylcholine)	3
Secretin (Class B)		3
Glutamate receptor (Class C)		7
Adhesion		5
Frizzled/Tas2		4

Abbreviations: GPCR, G-protein-coupled receptor

¹ Classification after [5].

^a Will likely also contain peptide receptors (see text).

^b Defined by sequence homology to known neuropeptide receptors [10].