The taxonomic state of bryozoan borings is analyzed in general, and Ropalonaria arachne (Fisher, 1866) is described accordingly. This find from the "Korallenoolith" (late Oxfordian, Upper Jurassic) of northern Germany is the first for the ichnogenus in Central Europe. The trace fossil was produced by ctenostome btyozoans boring in serpulid tubes in a high-energy environment. The ecology of the produsers is discussed; the animals avoided competition by their special choice of the substrate..