Balanoids gained their advantage over the chthalamoids in the Oligocene, when they evolved tubular skeletons, which provide better anchorage to the substrate, and allow them to grow faster, undercutting, crushing, and smothering the latter group.
Balanoids gained their advantage over the chthalamoids in the Oligocene. They evolved tubular skeletons. They was undercutting. They was crushing. They was smothering the latter group. Tubular skeletons provide better anchorage to the substrate. Tubular skeletons allow them to grow faster.