Ciliated ridges in the buccal funnel. (A) SEM of intact pilidium, viewed straight down the buccal funnel (bf). Inner ciliated band (icb) cilia point inward; buccal ridge (br) cilia point into exhalant gutter (ex) and outward, toward posterior lobe (pl). (B) Cracked pilidium exposing buccal ridges; right buccal ridge (br, lower one in figure) is cracked just above trunk disc (td). Cilia of both ridges point toward exhalant gutter (ex). (C) Pilidium cracked to expose the joint between inner ciliated band (icb) and buccal ridge (br). Cilia point in different directions, with a clear breakpoint. (D) View into the buccal funnel (Additional file 9: Video 9), showing beat orientation of buccal ridges (br) alongside exhalant gutter (ex); ms = circumesophageal muscle. Outset shows double-magnified frames at peak (forward stroke) and valley (just before recovery stroke). Kymograph (D’) of highlighted region shows that ciliary tips move backward almost as fast and far from the base as they do forward, suggesting the “resting” beat may achieve little net flow. (E) Pilidium trapped between slide and coverslip (Additional file 10: Video 10); although the lappets cannot flap well, at high density cells often blunder into the vestibule. This larva “notices” the cell (arrowhead), then accelerates buccal ridge (br) beat; this apparently initiates flow, drawing prey toward stomach (st) entrance. Tracings illustrate how the ridges are drawn backward, the funnel opens up, and the exhalant gutter clenches shut as the ciliary beat accelerates (top and bottom highlight before and after). Kymograph (E’) made just ahead of the buccal ridge indicates that the metachronal wave speeds up by ~3-fold. (F) Frame sequence in which a pilidium rejects a polystyrene bead (arrowhead); the object exits the buccal funnel through the buccal ridges, down the exhalant gutter (ex) below the stomach (st), and underneath the posterior lobe (pl).