zona pellucida

https://doi.org/10.1351/goldbook.11392

Acellular glycoprotein-rich membrane surrounding the mature ovum.

Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 822 (https://doi.org/10.1515/pac-2015-1202)