Genus-level relative frequency changes, based on scolecodont data, show that the polychaete faunas went through dramatic turnovers during the Llandovery–Wenlock Ireviken Event on Gotland. In addition several taxa show range ends (FADs and LADs) and gaps in this interval; at least 20% of the lineages disappeared or became extinct during the event. Datum points 2 and 4 seem to have been particularly harsh. This is the first detailed data set showing the effects of the Ireviken Event on vagrant benthos.