ULTRASTRUCTURE OF THE FEEDING APPARATUS AND MYONEMAL SYSTEM OF THE HETEROTROPHIC DINOFLAGELLATE PROTOPERIDINIUM SPINULOSUM1

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  • 1

    Received 13 June 1991. Accepted 11 October 1991.

  • We thank O. R. Anderson for his valuable suggestions and U. K. Stoecker for use of her rotating apparatus. This work was supported by the Woods Hole Oceanographic Institution Education Office and National Science Foundation grants OCE-8400292 and OCE-8911226. This is contribution no. 91017 from the Bigelow Laboratory for Ocean Sciences and contribution no. 7713 from the Woods Hole Oceanographic Institution.

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ABSTRACT

The feeding veil or pallium of the thecate heterotrophic dinoflagellate Protoperidinium spinulosum Schiller is a highly vesiculate membranous sac containing several arched, sometimes bifurcated microtubular ribbons. It originates from an internal microtubular basket, passes through a sphincter-like osmiophilic ring located inside the posterior flagellar pore, and emerges from the cell at that pore. The osmiophilic ring is part of an interconnected myonemal system (composed of two striated collars and several striated connectives) that is anchored to the pore plate and to two inward protrusions composed of minute sulcal plates. A related species, Protoperidinium punctulatum (Paulsen) Balech, also possesses a microtubular basket/osmiophilic ring complex. Elongate electron-dense bodies within the basket resemble digestive secretory granules found in other protists. Granular, electron-lucent microbodies clustered at the anterior end of the basket may also have a role in prey digestion. Dense membranous whorls observed within a P. spinulosum cell presented as it was preparing to initiate feeding indicate a condensed storage site for pallium membranes. A narrow microtubule-strengthened pseudopodal appendage found in two non-feeding cells constitutes the tow filament that serves as the initial linkage between the dinoflagellate and its food. The structures that constitute the pallium and pallium precursors, described here for the first time, are unlike those of other known protists, although some similarities with the dinoflagellate peduncle are evident. The existence of this unique system of organelles may have important ramifications in the search for evolutionary relationships among protists.

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