A time lapse series of contractions in a fused twin pair of clonal individuals of Tethya wilhelma (Demospongiae). This movie was taken approximately two weeks after the specimens were brought together to fuse. Mind the paradoxon concerning regulation of the visible morphological changes: while bothe specimens retain their own contraction rhythm, the expansion and retraction of the body filament is perfectly synchronized in both specimens. How to explain this? Some details of this questions are addressed in my publication Nickel, M. (2004), "Kinetics and rhythm of body contractions in the sponge Tethya wilhelma (Porifera: Demospongiae)", Journal of Experimental Biology, 207: 4515-24.
Copyright by M. Nickel; no unauthorised copying, distribution or broadcasting. Feel free to use it for teaching purpose.