• Amphidinium cryophilum;
  • dinoflagellate;
  • Dinophyceae;
  • phagopod;
  • phagotrophy;
  • Pyrrophyta;
  • ultrastructure


The cold-water, photosynthetic dinoflagellate Amphidinium cryophilum Wedemayer, Wilcox & Graham feeds phagotrophically on other dinoflagellate species. Food is ingested through a feeding tube, termed here the “phagopod,” which extends from the antapex. The peduncle of this organism plays no observable role in the feeding process. The phagopod is essentially a hollow cylinder composed electron-opaque material that is possibly deposited on a membrane. No Amphidinium cytoplasmic components, including microtubules or other cytoskeletal elements, were observed in the phagopod. Prefeeding cells aggregate, in small clumps near prey organisms with their phagopods extended. Eventually some cells commence feeding, first inserting the phagopod through the prey cell-covering and then slowly, over a period of 10 min or more, drawing cytoplasm through the phagopod and into a nascent food vacuole. Both light and electron microscopy suggest that one or more prey cell amphiesmal membranes remain intact during the feeding process. Upon completion of feeding, the Amphidinium cell swims off with a prominent food vacuole in the hypocone, leaving at least part of the phagopod attached to the prey cell. Phagotrophy in A. cryophilum seems to vary with light intensity. At low light intensities, cells feed phagotrophically and are nearly colorless, whereas at high light levels they feed much less frequently, if at all, and are brightly pigmented.