A new endolithic boring (Pinaseocladichnus perplexus isp. nov.) has been documented in brechiopods (orthids) shella coming from Lower Ordovician Oretan shales (approx. Early "Llanvirn") of the Toledo Mts., central Spain. The ichnofossils are preserved as natural moulds after dissulution of shell substrates, allowing its detailed study and illustration with SEM. Structures of this species cam be certainly compared with borings of ctenostomate bryozoans (Stolonifera): P. perplexus isp. nov. is therefore the oldest evidence of boring activity whithin this group. The colonization of the shells by bryozoans occurred most probably during brachiopods life, settling preferably in the marginal area (anterior and lateral) at shallow levels inside the dorsal valves.