The CCK/gastrin family appears to be represented in the whole chordate phylum, and in addition to mammals, CCK and gastrin have recently been identified in a number of nonmammalian species representing the major vertebrate classes, including fishes, amphibians, reptiles, and birds.     ///    Phylogeny of the cholecystokinin/gastrin family..     ///    This now makes it possible to consider the CCK/gastrin phylogeny based on structural information.     ///    "Instead, CCK/gastrin-specific antibodies might be cross-reacting with Asp-Phe-amides, like the lymnaDFamides, isolated from the freshwater snail Lymnaea stagnalis. "    ///    "Although the occurrence of CCK/gastrin-related peptides has been suggested in representatives of several invertebrate phyla, the evidence, mostly based on immunoreactivity, has not been substantiated by peptide identification. "    ///    "Cionin, isolated from Ciona intestinalis, a representative of the protochordates that occupy a key position at the transition to vertebrates, so far represents the oldest genuine member of the CCK/gastrin family, dating the emergence of these peptides back to at least 500 million years ago. "    ///    "The overall gene structure, including exon/intron organization, is similar in all mammalian and nonmammalian CCK/gastrin genes. "    ///    "In conclusion, the CCK/gastrin family appears to be represented in most, if not all, chordates, to which group it may also be limited. "