What was a group of mollusks that became more abundant and inprotant part of the reefs?

A group of mollusks that became more abundant and important in reef ecosystems are bivalves, particularly oysters and clams. These organisms play crucial roles in reef health by filtering water, thus improving water quality, and providing habitat for various marine species. Their presence contributes significantly to biodiversity and can enhance the structural complexity of reef environments. Additionally, bivalves can form extensive reefs themselves, further supporting marine life.