Previous studies have suggested several adaptive functions for the decorated tube caps of Diopatra cuprea (Polychaeta: Onuphidae). We experimentally tested the hypothesis that decoration provides crypsis. A series of field experiments quantified predation-related damage done to tube caps that were (1) devoid of decoration, (2) decorated with algae, or (3) decorated with shell fragments. If decoration provides crypsis, then undecorated tube caps should experience more damage than decorated tube caps; this pattern was not observed. Decoration may still reduce predation rates by means other than crypsis, but these results strongly suggest that tube decoration does not interfere with predator recognition of D. cuprea tube caps and that crypsis is consequently not important in this system.