Summary
The ultrastructure of the pusule apparatus has been investigated in some 40 dinoflagellates from both feshwater and marine environments. The morphology of the organelle is varied and seven more or less distinct types have been identified. These can be grouped into two categories:
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a)
Pusules with pusule vesicles: vesicles opening directly into the flagellar canal; vesicles opening into a collecting chamber which branches from the flagellar canal; pusule with internal collecting chamber surrounded by vesicles; complex tubular pusule with vesicles.
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b)
Pusules constructed of tubules or sack only: simple tubular pusule which may have a collecting chamber; tubular pusule with invaginations of the walls; sack pusule with invaginated walls.
A characteristic feature of the structure of the vesicles, when present, and of the tubules and sacks is the two-membrane nature of the 14–20 nm thick wall. This is constructed of plasma-membrane, invaginated from the flagellar canal, to which is appressed a vacuolar membrane. The vesicles and tubules are always surrounded by extensions of the cell vacuolar system. Various hypotheses concerning the function of the pusule are discussed and it is concluded that it is most likely an excretory or osmo-regulatory organelle.
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Dodge, J.D. The ultrastructure of the dinoflagellate pusule: A unique osmo-regulatory organelle. Protoplasma 75, 285–302 (1972). https://doi.org/10.1007/BF01279820
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DOI: https://doi.org/10.1007/BF01279820