Large trace fossils attributed to the ichnogenus Psilonichnus (Fürsich) have been identified in subtidal sediments of the Red Crag Formation (late Pliocene) of Walton-on-the-Naze, Essex, U.K. The traces are vertical or inclined, tapering cylindrical structures, occasionally branched, up to 2.3 m long. The structures are mud-rich relative to the surrounding sediment and their fills often show a spiralling grain fabric. The ichnogenus Psilonichnus has formerly been attributed to the burrowing activities of intertidal and supratidal crab species. The known fossil crab assemblage of the Red Crag contains no deep burrowing species. The traces are thus attributed to other crustaceans, possibly thalassinidean shrimps. The occurrence indicates that Psilonichnus may have a greater palaeoenvironmental range than previously realized.