The Fox genes encode a group of transcription factors that contain a forkhead domain,which forms a structure known as a winged helix.These transcription factors play a crucial role in several key biological processes,including development.High-degree identity in the canonical forkhead domain has been used to divide Fox proteins into 23 families(FoxA to FoxS).We surveyed the genome of three spiralians,the oyster Crassostrea gigas,the limpet Lottia gigantea,and the annelid Capitella teleta.We identified 25 C.gigas fox genes,21 L.gigantea fox genes,and 25 C.teleta fox genes.The C.gigas fox and L.gigantea fox genes represented 19 of the 23 families,whereas FoxI,Ql,R,and S were missing.The majority of the Fox families were observed within the C.teleta fox genes,with the exception of FoxR and S.In addition,the foxAB-like gene,foxY-like gene,and foxH gene were also present in the three genomes.The conserved FoxC-FoxL1 cluster,observed in mammals,was also found in C.gigas.The diversity of temporal expression patterns observed across the developmental process implies the C.gigas fox genes exert a wide range of functions.Further functional studies are required to gain insight into the evolution of Fox genes in bilaterians. The Fox genes encode a group of transcription factors that contain a forkhead domain, which forms a structure known as a winged helix. These transcription factors play a crucial role in several key biological processes, including development. High-degree identity in the canonical forkhead domain has been used to divide Fox proteins into 23 families (FoxA to FoxS). We surveyed the genome of three spiralians, the oyster Crassostrea gigas, the limpet Lottia gigantea, and the annelid Capitella teleta. 25 identified. gigas fox genes, 21 L. gigantea fox genes, and 25 C. teleta fox genes. The C. gigas fox and L. gigantea fox genes represented 19 of the 23 families, while FoxI, Ql, R, and S were missing. The majority of the Fox families were observed within the C. teleta fox genes, with the exception of FoxR and S. In addition, the foxAB-like gene, foxY-like gene, and foxH gene were also present in the three genomes. The conserved FoxC- FoxL1 cluster, observed in mammals, was also found in C. gigas. diversity of temp oral expression patterns observed across the developmental process implies the C. gigas fox genes exert a wide range of functions. Further functional studies are required to gain insight into the evolution of Fox genes in bilaterians.