zona pellucida A glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but not extraneous to it. The zona pellucida first appears in multilaminar primary oocytes. BTO:0003135 EHDAA2:0002220 EHDAA:31 EHDAA:62 EMAPA:16035 FMA:18674 GAID:410 MA:0001715 MESH:D015044 NCIT:C33896 Outside the plasma membrane, three envelopes surround the ovum. The first, the primary egg envelope, lies between the plasma membrane and the surrounding cells of the ovary. The most consistent component of this primary layer is the vitelline membrane, a transparent jacket of fibrous protein. In mammals, the homologous structure is called the zona pellucida.[well established][VHOG] TAO:0001111 UBERON:0000086 UMLS:C0043519 VHOG:0000720 ZFA:0001111 oolemma pellucid zone striated membrane uberon vitelline envelope vitelline membrane zona pellucida - vitelline membrane zona radiata zona striata acellular anatomical structure