Micropyle

Definition

A small, specialized pore or differentiated region in the chorion of an arthropod egg through which sperm enters to achieve fertilization; typically located at or near the anterior (cephalic) pole and often associated with specialized sculpturing, canals, or aeropyles that guide sperm to the oocyte membrane.

Etymology

Greek mikros (small) + pylē (gate, entrance)

Example

In many Lepidoptera, the micropyle appears as a distinct circular or slit-like depression surrounded by a raised annular ridge on the egg's anterior pole; in some spiders, multiple micropyles may be scattered across the egg surface.

Related Terms

• Chorion
• aeropyle
• oocyte
• spermatheca
• Fertilization
• oviposition
• egg sculpturing
• micropylar canal

Usage Notes

Distinguished from aeropyles, which are respiratory pores for gas exchange; micropyles are strictly reproductive structures. In insects with sperm storage (spermatheca), the micropyle allows entry of sperm from the exterior, whereas in some arachnids with direct sperm transfer, the micropyle may be reduced or absent. The term is also used in botany for the opening in seed plant ovules, but the zoological sense is primary in entomology. Micropyle number, position, and morphology are important taxonomic characters in egg identification, particularly for parasitoid wasps and moth eggs.