Polychaete jaw apparatuses, until recently very rare in fossil state, have been discovered in large numbers in the Ordovician and Silurian limestone of the Baltic Region. Investigations on them (Kielan-Jaworowska 1966) have shown that the systematics of polychaete annelids based on jaw apparatuses is close to natural and that the jaw apparatuses are important as index fossils. It is stressed that combining the parataxonomy of scolecodonts with the systematics of jaw apparatuses in one system makes it impossible to carry out any meaningful scientific investigation in this field. An attempt is made to explain the scarcity of polychaete jaws in Mesozoic and Tertiary deposits.