One of the most abundant forms of bioerosion sculpture on Mesozoic and Cainozoic shells and other hard substrates has a pentaradiate symmetry based on a regular, stellate module consisting of five radiating grooves. Regular echinoids today, browsing on encrusting and boring organisms on hard substrates, produce identical sculpture to the trace fossil, and a common origin is suggested. The tooth scratches lose their pentaradiate orientation and become subparallel where the echinoid gnaws along edges of shells and flat pebbles; a corresponding sculpture is also encountered in the trace fossil. The pentaradiate trace fossil is designated as Gnathichnus pentax, ichnogen. et ichnosp. nov.