Apheloria corrugata

The millipede Apheloria corrugata secretes a mixture of HCN and benzaldehyde to prevent other animals from eating it. The millipede stores mandelonitrile (benzaldehyde cyanohydrin) in a reservoir. When attacked, it discharges mandelonitrile through a reaction chamber containing enzymes that catalyze the conversion of the cyanohydrin to benzaldehyde and HCN. 

The millipede Apheloria corrugata, as well as other species, produces hydrogen cyanide and benzaldehyde by enzymatic decomposition of the cyanohydrin adduct, mandelonitrile (equation 10.1). One can question Why benzaldehyde since all normal aldehydes add hydrogen cyanide reversibly across the C = O double bond. However, to the human nose at least, HCN and benzaldehyde have... 

The isolation of the glucoside of cuminaldehyde cyanohydrin (XCVI) from the millipede Polydesmus vicinus L. [732] is of great interest since, like the established function of mandelonitrile in Apheloria corrugata [733-735] it could represent a means of delivery of hydrogen cyanide. 

Benzaldehyde cyanohydrin (mandelonitrile) provides an interesting example of a chemical defense mechanism in the biological world. This substance is synthesized by millipedes (Apheloria corrugata) and stored in special glands. When a millipede is threatened, the cyanohydrin is released from the storage gland and undergoes enzyme-catalyzed reversal of cyanohydrin formation to produce HCN, which is then... 

Despite, or perhaps because of, the high toxicity of cyanide, cyanohydrins are widely distributed in nature. The cyanohydrin of benzaldehyde, PhCH(OH)CN, is used as a defense mechanism by the millipede Apheloria corrugata. When the millipede is attacked, it excretes the cyanohydrin, which is then enzymatically converted to benzaldehyde and HCN, the latter being toxic to the attacker. 

Cyanohydrin chemistry plays a central role in the defense system of Aphelo-ria corrugata. This millipede uses a two-chamber gland much like that used by the bombardier beetle (see A Word About... Quinones and the Bombardier Beetle in Chapter 7) to deliver a secretion that contains hydrogen cyanide. Apheloria stores benzaldehyde cyanohydrin and, when threatened, converts it to a mixture of benzal-dehyde and hydrogen cyanide, which is then secreted. The hydrogen cyanide gas that emanates from the secretion is an effective deterrent of predators. 

---