A CRYPTHECODINIUM COHNII-LIKE DINOFLAGELLATE FEEDING MYZOCYTOTICALLY ON THE UNICELLULAR RED ALGA PORPHYRIDIUM SP

A Crypthecodinium cohnii-Like dinoflagellate was found to prey on the unicellular red alga Porphyridium sp. The cytoplasm of the prey is ing ested by myzocytosis within 10-30 s, and the contents of up to 20 Porp hyridium cells tan be taken up by one dinoflagellate. The heeding tube is retracted after each uptake process. Cytochalasin D disturbs the s uction and the retraction of the heeding tube. Feeding behaviour depen ds on the light-dark regime: the dinoflagellates prey preferentially i n the dark period and finish the trophic phase at the beginning of the light period. They then assemble and encyst, and digestion takes plac e in the light period. Cell. division is restricted to the encysted st age. At the end of the light period excystment takes place, combined w ith defecation. Isogamy as well as anisogamy and nuclear cyclosis were observed. The trophonts have very thin thecal plates and a microtubul ar basket with two kinds of elongate vesicles. The microtubules of the tubular basket are also found in young cysts, formed after the end of the feeding period. The fine structure of the digestion vacuoles and of the faecal bodies is described.