A wall-shaped, (sub)horizontal, unbranched burrow with a passive filling cannot exist, because a wall-shaped burrow cannot be produced without moving the original burrow vertically. This replacement of the burrow tube will always result in an active filling of older burrow parts.

However, never say never... If you are sure that you did not do any mistakes in determining your trace fossil so far, please describe your probably new trace fossil genus and send us a pdf of your publication. We will then incorporate it into our determination key, here. Thank you for your help!