Cilia are specifically involved in the sponge behaviour. a. In contrast to Neomycin sulfate (solid red) which eliminates the ‘sneeze’ response (n = 3, p = 0.035), the calcium channel blocker Verapamil (dotted red) does not affect amplitude of the sneeze behaviour in S. lacustris (n = 5, p = 0.573). b. Texas-Red Neomycin sulfate conjugate (red) and YO-PRO1 (green) selectively label cells in the osculum. c. A 20 hr treatment in chloral hydrate eliminates the sneeze behaviour in S. lacustris (solid green; n = 5, p = 0.004), which does not return until more than 3 days after recovery (dotted green; n = 5, 24 hr washout p = 0.003, 72 hr washout p = 0.018, 120 hr washout p = 0.864)). d-f(SEM) d’-f’(fluorescence). Cilia are removed by chloral hydrate treatment; S. lacustris 0 hr (d, d’), 20 hr (e, e’), and 70 hr (f, f’) treatment in chloral hydrate. g. The sneeze behaviour in S. lacustris cannot be triggered when the osculum is removed (solid blue; n = 3, p = 0.010) until it has fully regrown (dotted blue; n = 3, p = 0.275). h. Ciliated cells on the surface of E. muelleri 8 hr post osculum removal and (i) in the newly formed osculum 24 hr post osculum removal. Ciliated cells do not become labeled with EdU until after the osculum has regrown suggesting they arise by migration of newly formed mesohyl cells which differentiate into ciliated pinacocytes. Cilia are labeled with acetylated α-tubulin (red), nuclei with Hoechst (blue), and newly synthesized DNA with EdU (green). Scale bars: b, 50 μm inset 10 μm d, e, 5 μm d’, e’, f, f’, h, i 10 μm.