An informal name applied loosely to any indefinite traillike or tunnellike sedimentary structure identified as a trace fossil but not referred to a described genus. It was once considered to be the remains of the marine alga Fucus, and later was regarded as a feeding burrow of a marine animal and assigned to the plantlike genus Fucoides. The term has been broadly applied to crustacean tracks, worm burrows, molluscan trails, marks made by the tide or waves, and rill marks.