When considering zooplankton feeding as one of the pathways involved in the transfer of substances in marine ecosystems, it is important to study the composition and size distribution of the seston: firstly, the elements in which one is interested may be associated with different types and sizes of particles; secondly, particle size and composition are important factors in relation t o the feeding process of the zooplankton itself. High speed cinematographic studies have recently revealed that copepods use two different mechanisms for feeding. Small particles (< 12 pm) are collected by continuous low amplitude movements of the second maxillae and combing of the appendages. Larger particles are detected and collected individually by means of...