Pedal serotonergic neuron clusters of the pteropod mollusc, Clione limacina, contain two morphological subtypes with different innervation targets.

Each pedal ganglion of the pteropod mollusc Clione limacina contains a cluster of serotonin-immunoreactive neurons that have been shown to modulate contractions of the slow-twitch musculature of the wing-like parapodia, and contribute to swim accelerations. Each cluster has a variable number of neurons, between 5 and 9, but there is no significant difference between right and left ganglia. In experiments with electrophysiological recordings followed by dye-injection (carboxyfluorescein), the clusters were found to contain two subsets of neurons.