The content of fecal pellets of the freshly collected warm water appendicularian Megalocercus huxleyi was studied by light and electron microscopy and by flow cytometry in the superficial 100 m of the water column at 2 ¿N, 165 ¿E, in September 1994, during the Flux dans l'Ouest du Pacifique Equatorial (Joint Global Ocean Flux Study-France) oceanographic cruise. Microscopic observations showed that the fecal pellet contents of M. huxleyi reflected the natural composition of the nanophytoplankton and small microphytoplankton (7% of the small particulate matter will be daily removed from the water. Some of this matter will be assimilated, some trapped in the houses, and the rest aggregated into rapidly sinking fecal pellets. Ingestion of large quantities of coccolithophorids indicates that appendicularians are important not only in the cycle of organic carbon but also of inorganic carbon. Moreover, if appendicularians successfully aggregate and assimilate Prochlorococcus and picoeucaryotes, then their grazing activity can represent a major pathway of carbon transformation in the tropical ecosystem. ¿ 1999 American Geophysical Union