Arthropods do not have one, but two genes encoding an allatostatin C-like peptide. The newly discovered paralog gene was called Ast-CC, and the peptide which it is predicted to make was called allatostatin double C (ASTCC). Genes for both allatostatin C (ASTC) and its paralog were found in the tick Ixodes scapularis as well as dipteran, lepidopteran, coleopteran, aphidoidean and phthirapteran insect species. In addition partial or complete cDNAs derived from Ast-CCs were found in a number of species, including Drosophila melanogaster, Bombyx mori and Rhodnius prolixus. The ASTCC precursors have a second conserved peptide sequence suggesting that they may produce two biologically active peptides. The predicted precursors encoded by the Ast-CCs have some unusual features, particularly in Drosophila, where they lack a signal peptide, and have instead a peptide anchor. These unusual structural features suggest that they are perhaps expressed by cells that are not specialized in neuropeptide synthesis and that in Drosophila ASTCC may be a juxtacrine. Data from the Fly Atlas project show that in Drosophila Ast-CC is little expressed. Nevertheless a P-element insertion in this gene is embryonic lethal, suggesting that it is an essential gene. Similarity between the precursors and receptors of ASTC/ASTCC and somatostatin suggests that ASTC/ASTCC and somatostatin have a common ancestor.