WIDESPREAD PHAGOCYTOSIS OF CILIATES AND OTHER PROTISTS BY MARINE MIXOTROPHIC AND HETEROTROPHIC THECATE DINOFLAGELLATES

An electron microscopic examination of large amorphous inclusions loca ted in a variety of photosynthetic thecate dinoflagellates (Alexandriu m ostenfeldii (Paulsen) Balech et Tangen, Gonyaulax diegensis Kofoid, Scrippsiella sp., Ceratium longipes (Bailey) Gran, and Prorocentrum mi cans Ehrenberg) and a nonphotosynthetic thecate species (Amylax sp.) r evealed each inclusion to be a food vacuole, the majority of which wer e ingested ciliate prey. Recognizable features of these ciliates inclu ded linear arrays of basal bodies and cilia consistent with oligotrich polykinetid structure, characteristic macronuclei, chloroplasts (evid ently kleptoplastids), cup-shaped starch plates, and cylindrical extru somes. Three species contained (apparent) nonciliate prey: Scrippsiell a sp., whose food vacuoles consistently contained unusual and complex extrusome-like cylindrical bodies having a distinctive six-lobed, mult ilayered structure; P. micans, which contained an. unidentified encyst ed cell; and a single A. ostenfeldii cell, containing a Dinophysis sp, dinoflagellate cell. Several food vacuoles of ciliate origin had a re d hue. This, together with the resemblance of A. ostenfeldii cells to planozygotes, suggests that similar structures previously identified a s accumulation bodies may in fact be food vacuoles and that feeding ma y in some cases be associated with sexual processes.