Ciliary motility in ciliates such as Paramecium or Tetrahymena is the mechanism by which cellular behaviour is regulated and on which survival depends. As a consequence, protozoan cilia have elaborate sensing systems built into them, probably by intraciliary transport
(ICT-orthologous to intraflagellar transport). As a response to stimuli, 2nd messenger concentration around the axoneme increases. A unifying hypothesis suggests that for rapid responses the 2nd messengers act on axonemal dynein to change the rates of doublet sliding, which in turn affects ciliary
parameters that control behaviour.