Figure 1.

Opening and closing of the trapdoor of U. stellaris and related flows. (a) Diagram of U. stellaris bladder. Arrow shows opening of the trapdoor. (b) Summary of prey capture in U. stellaris including timescales measured in this study. Following an unsuccessful capture, the trap resets in approximately 20–30 min (1). When the trigger hair are mechanically stimulated by prey, the trap door opens in 300–700 µs (2) to generate strong suction flows that capture (3) and digest (4) prey. (c) Trap-resetting phase. Plot shows how the closed bladder generates lower than ambient internal pressures. The x-axis indicates time elapsed since the last successful activation of the trapdoor and the y-axis indicates the external (higher)–internal (lower) pressure of the bladder. The break in axis and plots indicates post-stabilization of internal pressure, the trap can be retriggered after any arbitrary time duration to rapidly bring it back to zero state. (d) Opening and closing kinematics of the trapdoor. Trapdoor kinematics is depicted as a ratio of area of the open mouth to a reference rim area with time. Grey lines show 10 individual plots normalized to maximum ratio of areas (for a fully open trap), the dark black line shows the normalized average curve of these 10 plots. The dashed black line shows the average time point of bladder opening. (e) Opening and closing phase. Four frames from a video capture show U. stellaris trapdoor in the following stages: (i) initiation of opening, (ii) fully open, (iii) before closing, and (iv) fully closed. Numbers in the lower left corner of each figure indicate time (microseconds) elapsed since initiation of door opening. The door hinge (dotted line) and margin (continuous) are labelled in panel (i). Typical diameter of the trap door is 0.8 mm.