CYPHONAUTES' CILIARY SIEVE BREAKS A BIOLOGICAL RULE OF INFERENCE

Biologists routinely assume that a mechanism demonstrated in one organism will be found in others in which form, function, ancestry, and physical parameters are similar. These criteria failed to predict the feeding mechanism of the cyphonautes larva of bryozoans. Larval and adult bryozoans feed with cilia similar in size and distribution, with similar current velocities, and similar Reynolds numbers. Nevertheless, the larvae filter particles with a sieve of stationary cilia whereas the adults respond to individual particles with an induced local reversal of ciliary beat and concentrate particles without filtration. The larva's ciliary sieve is doubly unexpected because it requires a ciliary stiffness at the maximum recorded for cilia.