 Conserved positions of multiple introns in its gene and those of our arrestin subtypes suggest that they all evolved from this ancestral arrestin.Lower invertebrates, such as roundworm "C. elegans", also have only one arrestin.Insects have arr1 and arr2, originally termed “visual arrestins” because they are expressed in photoreceptors, and one non-visual subtype (kurtz in "Drosophila").