We examined the hooked setae of a dominant group of tube-dwellers, the polychaete annelids, and found a pattern of setation that is predictable by tube type, exclusive of worm taxon or orientation; we also demonstrated the mechanical significance of these hooked setae. When tube-dwelling worms belonging to different lineages are pressurized, they resist differentially as a function of the direction in which hooks face. The results are consistent with the hypothesis that hooks are used primarily to resist removal of worms from their tubes, are polyphyletic in origin, and are active agents of resistance.
© 1987 The Society for the Study of Evolution.