The Upper Jurassic coral colonies collected from glacial deposits in northern Poland reveal abundant boring and nestling organisms. The most common borers were bivalves, among which 4 gastrochaenid species (Gastrochaena s. s. and Spengleria) and 2 lithophagid species are described. Other borers included sipunculid worms and sponges (7). The nestling fauna consists of the bivalves Hiatella (probably also a facultative borer), Plicatula, and oysters, as well as serpulids. The assemblage of borers is suprisingly similar to Recent assemblages from coral reefs. The excellent preservation of aragonitic bivalve structures allowed for a detailed examination of the internal structure of shells and boreholes. Basing on these features, new diagnostic characters are here proposed and a partial revision is undertaken.

Key words: Boring organisms, bivalves, taxonomy, Upper Jurassic, Poland.