Omega-3 fatty acids occur as triglycerids, as diglyceride with a phosphate group (phospholipids) or as sphingomyelin, which is derived from sphingosine instead of glycerol. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from sphingosine instead of glycerol.