A single specimen of an enigmatic new attachment etching,together with an unknown calcareous encruster partly preserved in situ, hasbeen identified on a belemnite rostrum from the Marnes de Dives Formation(Callovian, Middle Jurassic) of the Falaises des Vaches Noires in Normandy,France. The trace fossil, here established as the new ichnotaxonCircumpodichnus serialis igen. et isp. n., is a uniserial arrangement of very shallow depressions,oval to fusiform in outline, with peripheral pouches and central pits.

The trace maker has a morphology unlike any other known calcareous epibiont,fossil or recent, and is consequently described as the newmicroproblematicum Circumpodium enigmaticum gen. et sp. n. Its calcitic skeleton is composed of achain of segments with perforate basal and lateral walls, anchored to theattachment trace in the substratum by vertical protrusions in the centre andfeet-like protrusions in the periphery. The hypothetical upper wall of thesegments was either organic-walled and has decayed or it was calcitic andhas been abraded.

Based on morphological criteria and the capacity to bioerode, C. enigmaticum can best becompared to encrusting bryozoans and foraminiferans. Candidate bryozoans areaberrant arachnidiid ctenostomes, early cheilostomes, or stomatoporidcyclostomes. Among the foraminiferans, webbinellid or ramulinidpolymorphinids are closest in their characters. In addition, tintinnid orfolliculinid ciliophorans are considered as an alternative interpretation,and similarities to the Palaeozoic microproblematicum Allonema are discussed.