At their peak in the Paleozoic era , the brachiopods were among the most abundant filter-feeders and reef-builders , and occupied other ecological niches , including swimming in the jet-propulsion style of scallops .
At their peak in the Palaeozoic era the brachiopods were among the most abundant filter-feeders and reef-builders , and occupied other ecological niches , including swimming in the jet-propulsion style of scallops .