Arachnostega n. ichnog. -burrowing traces in internal moulds of boring bivalves (late Jurassic, northern Germany)

Burrowing traces in internal moulds of molluscs are described as Arachnostega gastrochaenae n. ichnog, n. ichnosp. Currently, the ichnogenus is only known from the Late Jurassic and Recent of Northern Germany. The synecology of its polychaete producers is discussed in detail: they were probably opportunistic detritus-feeders and have to be regarded as infaunal coelobites. The tracemakers were not part of an ecological succession because their activity was facilitated by a sedimentation event. They weakened the skeletal frame but rapid cementation and encrusters inhibited them. Finally, aspects of biostratinomy and fossil diagenesis are sketched.