Feeding in Peridiniopsis berolinensis (Dinophyceae): new observations on tube feeding by an omnivorous, heterotrophic dinoflagellate

Peridiniopsis berolinensis (Lemmermann) Bourrelly (Peridiniales, Dinophyceae) is attracted to injured or dying protists (including other dinoflagellates and cells of its own kind) and small metazoans. Punctured nematodes were used for experimental induction of feeding. Peridiniopsis berolinensis uses a filament to establish connection with potential food items and ingests their fluid contents through a feeding tube protruded from the mid-ventral region of the cell. Food items small enough to pass through the tube can be ingested whole. The feeding tube is supported by c. 20 rows of microtubules, and is lined by a single membrane, continuous with the plasma membrane and with the membrane of the forming food vacuole. The tube and the longitudinal flagellum pass through a sulcal cavity lined by amphiesmal plates that shows an unusual fibrous connection between the edge of a plate and the middle of another. Suction seems to be involved in food uptake, and it is proposed that the driving force is mechanical generation of lower pressure inside the food vacuole. This idea is supported by morphological changes in the episoma of pre-feeding cells. The membrane of the feeding tube was not seen to establish an intimate association with the plasma membrane of prey organisms and, therefore, use of the term myzocytosis in connection with the feeding mechanism of P. berolinensis is discouraged.