part of part of bounding layer of bounding layer of in taxon egg cell Bilateria vitelline membrane AAO:0010332 XAO:0000030 A structure directly adjacent to the outer surface of the plasma membrane of an ovum. It is composed mostly of protein fibers, with protein receptors needed for sperm binding, binding to sperm plasma membrane receptors. The species-specificity between these receptors contributes to prevention of breeding between different species [Wikipedia]. A protective layer around the egg[FBbt]. Thin membrane enclosing and immediately adjacent to the ovum. Produced in the ovary.[AAO] TODO - consider GO CC request. GO:0030704-vitelline membrane formation considered a subclass of CC organization zona pellucida - vitelline membrane m. vitellina GAID:1318 zona pellucida relationship loss: part_of zygote (AAO:0010324)[AAO] MESH:D014817 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] FBbt:00000042 UBERON:0003125 yolk sac membrane Wikipedia:Vitelline_membrane BTO:0001450 acellular membrane