How did the gill apparatus of early agnathans help with feeding?

Early agnathans utilized their gill apparatus as a dual-purpose structure for both respiration and feeding.1

These early jawless vertebrates likely engaged in filter feeding, a process facilitated by their large gill cavities. As water was drawn into the mouth—likely through a sucking action—small organisms were pulled into the gill cavity along with the water used for breathing. The gill apparatus then functioned to strain these small organisms out of the water, directing them toward the food canal. This evolutionary adaptation allowed the gill structure to serve as a critical mechanism for nutrient intake in addition to its primary role in the respiratory system.1