Abstract: The abilities of Boeckella (Copepoda: Calanoida) to assimilate filamentous cyanobacteria and to control the abundance of cyanobacterial trichomes were tested in laboratory experiments with Boeckella triarticulata and B. hamata. When fed monocultures of Anabaena flos-aquae and Cryptomonas ovata palustris, adult female copepods of both species assimilated the cyanobacterium at less than half of the rate at which they assimilated the cryptomonad. B. triarticulata females significantly reduced the concen ration of Anabaena trichomes in the absence and in the presence of an equal biomass of Cryptomonas. These results are consistent with those of our other studies on the ability of Boeckella spp. to utilize filamentous cyanobacteria.