The left side of the figure shows schematic representations of the gene structures, with protein-coding exons shown as rectangles and introns shown as lines (with intron length stated underneath). The protein-coding exons are colour-coded to show regions that encode the N-terminal signal peptide (blue), the neuropeptide (red), monobasic or dibasic cleavage sites (green) and other regions of the precursor protein (grey). The right side of the figure shows how an intron interrupts the coding sequence of the neuropeptides, but the position of the intron is different for echinoderm PrRP-like peptides and bilaterian NPY/NPF-type neuropeptides. In genes encoding echinoderm PrRP-like peptides the intron interrupts the coding sequence in the N-terminal or central region of the PrRP-like peptide, with the intron located between the first and second nucleotides of the codon (phase one intron) for an alanine (A. planci) or glycine (S. purpuratus) residue and the position of the intron in the reading frame is therefore represented as +1. In contrast, in bilaterian NPY/NPF genes the intron interrupts the coding sequence for NPY/NPF-type peptides between the second and third nucleotide of the codon for the arginine residue of the C-terminal RF or RY dipeptide and the position of this phase two intron in the reading frame is represented as −1. Taxa are highlighted in phylum-specific colours: dark blue (Echinodermata), light blue (Hemichordata), purple (Chordata), red (Lophotrochozoa), yellow (Priapulida), green (Arthropoda), grey (Nematoda). Species names are as follows: Apla (Acanthaster planci), Spur (Strongylocentrotus purpuratus), Skow (Saccoglossus kowalevskii), Hsap (Homo sapiens), Ggal (Gallus gallus), Drer (Danio rerio), Bflo (Branchiostoma floridae), Obim (Octopus bimaculoides), Cgig (Crassostrea gigas), Hrob (Helobdella robusta), Pcau (Priapulus caudatus), Agam (Anopheles gambiae), Cele Caenorhabditis elegans.