Overlay images combining autofluorescence (red), immunoreactivity (yellow; antiserum directed against FMRFamide in a, b, f, and against serotonin in c, d, e) and nuclear labeling (blue) to reveal mushroom body neuropils in (a) Harmothoe areolata (b) Nepthys hombergii (c) Phyllodoce maculata (d) Tomopteris helgolandica and (e) Odontosyllis cf. fulgurans. The cell cortex of the brain of Lumbrineris cf. fragilis (f) is not considered indicative of mushroom body neuropils due to the homogeneous distribution of somata and the lack of a distinctive associated neuropil compartment. al anterior lobe, ey eye, gc globuli cells, og olfactory glomeruli, pl posterior lobe, Arrowheads mark the poorly delineated neuropil boundary in N. hombergii, dashed lines mark the boundaries of globuli cell aggregations. Arrow root of the circumesophageal connective. Scale bars: 80 μm.