Diagnosis: Sedilichnus having a cylindrical to subcylindrical form. Outer opening circular. On the inner opening there is a dominant lateral protrusion, making the opening crescent-shaped in outline. The margin is perpendicular to the substrate surface; distal part of walls may be straight or slightly rounded.

Description: Simple, always penetrative borings on the shell of Macoma calcarea, with wall morphology similar to morphotypes of S. simplex described above. The protrusion has the form of a rounded right to obtuse triangle. It is flat or weakly elevated and reaches 20–50% of the inner opening diameter. Length of the outer opening ranges from 1.46 to 4.55 mm; the inner opening (the diameter of the crescent) is 1.10 to 2.80 mm in size.