Analysis of the exon structure in the protein sequences was made for all eukaryotic Dispanins except E. siliculosus where no such information was found. The eukaryotic Dispanins have a conserved splice site in the intracellular loop that separates the two transmembrane helices into different exons ( Figure 4 ). This site is only missing in the S. mansoni Dispanin and the mouse Dspa2f genes. The vertebrate proteins of the DSPA and DSPB subfamilies only have these two exons whereas the whole DSPC subfamily and the DSPD1 proteins have an additional exon that codes for their N-terminus. The DSPD2 proteins that only are found in mammals seem to have lost their N-termini exon. All the classified B. floridae and S. purpuratus sequences has the corresponding splice site in the N-terminus, whereas the N. vectensis and M. brevicollis proteins has 3-6 and 7 exons respectively.