In motor pattern generating motor circuits, like that involved in molluscan feeding, we have classified neurons into specific types such as motoneurons, central pattern generator (CPG) neurons, modulatory interneurons and command neurons with the aim of ascribing individual functions to elements of the neural circuit (Benjamin & Elliott, 1989). Recent work on the pond snail Lymnaea suggests that these functional categories are far too simple to define the variety of roles carried out by identified neurons of the feeding circuit. For instance, motoneurons do not just mediate muscle contraction but play a key role in motor pattern generation. This is due to electrical coupling between CPG interneurons and motoneurons (Staras et al. 1998) and the modulation of their endogenous properties by serotonin (Straub & Benjamin, 2001). CPG interneurons initiate feeding as well being part of the oscillator mechanism (Kemenes et al. 2001). Command-like neurons can initiate feeding, but they also control detailed aspects of the motor pattern like the duration of a particular phase and the frequency of the feeding rhythm (Kemenes et al. 2001). These recent results suggest that the basic mechanisms involved in the control and generation of rhythmic motor behaviour are not the property of a single class of neurons, but are widely distributed across the neural network.