Chloroplasts of the diatom, Streptotheca thamesis, are considerably deformed when they pass the feeding tube of the parasitic dinoflagellate, Paulsenella sp. Nevertheless, chloroplasts resume their normal shape and structure inside the food vacuole. Even the chloroplast ER is partially preserved. The feeding tube channel of Paulsenella chaetoceratis is narrow (about 0.2 μm in diameter) and may be very long (generally 100 μm). The feeding tube invades a seta of Chaetoceros decipiens through the apical or a lateral aperture and elongates until reaching the cell body of the host. The host chloroplasts are ruptured when they pass the feeding tube. However, large stacks of thylakoids remain intact. Stability of diatom chloroplasts and thylakoid stacks may be important in plankton research, e.g. using chlorophyll determinations as a measure for biomass production.