Box and whisker plots of longitudinal occurrence of 50 European Rhyacophila species based on the longitudinal zonation index (see Supplementary Material C). The species are grouped by the six gill types known to occur in the European fauna. Groups with significantly different longitudinal distribution ranges are indicated by letters above the box and whisker plots. Boxes represent the 50^th percentiles, the whiskers extend to the 100^th percentile. Horizontal lines within boxes indicate median values.