Plasmanylethanolamine desaturase involved in plasmalogen biogenesis in the endoplasmic reticulum membrane. Plasmalogens are glycerophospholipids with a hydrocarbon chain linked by a vinyl ether bond at the glycerol sn-1 position, and are involved in antioxidative and signaling mechanisms. 1-(1,2-saturated alkyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = 1-O-(1Z-alkenyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(III)-[cytochrome b5] + 2 H2O a 1-O-hexadecyl-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = a 1-O-(1Z-hexadecenyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(III)-[cytochrome b5] + 2 H2O a 1-O-octadecyl-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = a 1-O-(1Z-octadecenyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(III)-[cytochrome b5] + 2 H2O a 1-O-(9Z-octadecenyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = a 1-O-(1Z,9Z-octadecadienyl)-2-acyl-sn-glycero-3-phosphoethanolamine + 2 Fe(III)-[cytochrome b5] + 2 H2O Lipid metabolism; fatty acid metabolism. Histidine box-1 and -2 together with other histidine residues are essential for catalytic activity. Belongs to the fatty acid desaturase CarF family.