It is suggested that, because of their relatively simple repertoires of behavior, polychaetes may be particularly useful in behavioral research. An interesting range of responses has already been described in these animals, including those involved in habitat selection, feeding, tube construction, escape from predators, fighting, pairing, swarming, commensalism, and learning. In at least lugworms and some other polychaetes, much of the behavior has been shown to consist of spontaneous cycles of activity triggered by internal pacemakers. So far, little attention has been paid to the role of the central nervous system, but extirpations of parts of it in nereids have produced interesting results. The feature of particular interest in the brains of several polychaete families is the presence of corpora pedunculata. The function of these lobes is unknown, but they are well developed in nereids and polynoids, which lead unusually active lives.