Latrophilins are cell surface proteins coupling an extracellular cell adhesion/interaction domain to a family B g-protein coupled receptor (GPCR) signaling domain. In vertebrates, multiple highly alternatively spliced paralogs exist and are expressed in the nervous system with synaptic localization. The C elegans orthologs,
lat-1 and
lat-2, have similar overall protein structure, but unlike the vertebrate orthologs are not highly alternatively spliced with only
lat-1 having two isoforms. We see
lat-1 expression in two main cell types: developing epithelia and neurons, localizing to the apical and presynaptic surfaces respectively. RNAi and deletion mutants show defects in embryonic elongation, pharyngeal development and reproductive organ formation, correlating with the expression in the epithelium of these tissues. In comparison,
lat-2 expression is limited to the arcade and
g1 gland cells with expression cycling during the molting period. Our data suggests a role for
lat-1, and possibly
lat-2, in the cell surface organization/reorganization of epithelial cells during development, possibly by selective targeting of exocytic vesicles, with a similar role at the synapses. In total, we have identified eight family B GPCR genes in C elegans: flamingo (
fmi-1/F15b9.7), two latrophilin-related proteins (
lat-1/B0457.1,
lat-2/B0286.2), two methuselah-related proteins (
mth-1/F31D5.5,
mth-2/F31D5.4), and three presumptive hormone receptors (
seb-1/C13B9.4,
seb-2/ZK643.4,
seb-3/C18B12.2). We have characterized the genomic structure by sequencing cDNAs and RT-PCR, evolution by sequence and domain comparisons, and expression of these genes. Our analysis of the evolution of this family indicates major alterations of domain structure and several duplication events prior to the metazoan radiation, leaving at least five orthologus branches between C elegans and H sapiens. In addition, our analysis of the family B members in recently duplicated species give a glimpse of the ongoing evolutionary processes that are occurring in these genes.