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The parasitic foraminifer Hyrrokkin sarcophagapredominantly infests the cold-water coral Lophelia pertusaand the co-occurring bivalve Acesta excavata, showing a commensal or parasitic behaviour. It occurs also on some other corals (e.g., Caryophyllia sarsiae), bivalves (e.g., Delectopecten vitreus) and sponges (Geodiasp.), typically in aphotic environments. The aim of the study is to describe its traces from various host substrates, to characterise its parasitic behaviour and to map the geographical distribution of the genus Hyrrokkin. Epoxy-resin casts of H. sarcophagatraces in A. excavata C. sarsiae, D. vitreusand L. pertusa,and of H. carnivoratraces in A. excavata, were SEM analysed. The boring pattern is in all cases characterised by a shallow groove of up to 7 mm in diameter (max. 2 mm deep), from which ‘whip’-shaped extensions protrude vertically into the substrate. In A. excavatathe foraminifer can …