Fig. 4. A cross-sectional view of the antennule flagella and setae during a flick. The lateral flagellum is rapidly flicked ventrally during the closing phase (towards the bottom of the figure) and opened more slowly. Aesthetascs are aligned such that fluid flows between rows. The medial flagellum is not actively moved and its plumose setae remain slightly below the lateral flagellum during the flicks. The location of the medial flagellum's simple setae shifts medio-laterally along the length of the flagellum.