1. the most primitive type of kidney found in the embryos of vertebrates and in some adult lower vertebrates
Usage: anatomy; biology; plural form

Examples

• The pronephroi develop early in vertebrate embryogenesis.
• In fish larvae, the pronephroi serve as the primary excretory organs.
• The pronephroi are eventually replaced by more advanced kidney structures.
• Biologists study pronephroi to understand kidney evolution.
• The pronephroi consist of simple tubules that filter waste.
• During development, the pronephroi appear before the mesonephroi.