Planktonic ciliates, primarily oligotrichs and tintinnids (Subclass Choreotrichia, Orders Choreotrichida and Oligotrichida) are important grazers of phytoplankton, heterotrophic flagellates, and to some extent, bacteria in the sea. Recent studies suggest that they graze a significant portion of the primary production in the smaller size categories. Some, perhaps most, of these planktonic ciliates have feeding behaviors which cannot be accounted for by simple filter feeding models. Using a combination of scanning electron microscopy, high-speed videomicroscopy, and manipulation of particle characteristics, prey capture and selection by oligotrichs and tintinnids can be experimentally investigated and analyzed. The questions to be addressed are: What are the relative roles of sieving (filter feeding), direct interception, hydrodynamic processes, and active scan and trap mechanisms in particle capture by the oral membranelles? How do the physiochemical properties of particles (size, density, surface charge and hydrophobicity) affect particle capture? Does post-capture selection occur? Does variation in particle capture mechanisms or selectivity occur among these ciliates? The integrated approach, which includes functional morphology, hydrodynamics and biophysics, will be useful in elucidating the feeding biology of marine planktonic ciliates.
