Mystery trace fossils

During my field research years ago in the Paleogene of the Southern Carpathians (Romania), I found these interesting trace fossils.  They are cylindrical, perpendicular to bedding, and always occur in pairs, suggesting they are U-shaped.  The hosting formation is Eocene in age, consists of silty mudstone deposited in a distal shelf environment and is bounded at the top by a sequence boundary, which occurs immediately above this burrowed interval.

© RomaniaRocks

© RomaniaRocks

My interpretation at the time was that the intensely burrowed interval suggests slow rates of sedimentation, which allowed organisms sufficient time for bioturbation.  Abrupt changes in habitat conditions (e.g. increased sediment content in the water column caused by landward subaerial exposure and erosion) destroyed the animal population.  The abandoned burrows were subsequently filled with sediment (e.g. fine sand and silt) during a time when sediment bypass occurred.

I was never able to clearly identify these trace fossils.  The closest I came to it was "Lanicoidichna", but I do not think this is correct.  A colleague suggested that this may be related to the jackknife clam Tagelus (see pictures here and here).

If you recognize these and can name the type of borrow, please let me know; it would be nice to be able to finally find an answer.