Page 142 - Algae Anatomy, Biochemistry, and Biotechnology
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Anatomy 125
FIGURE 2.82 Ejectile organelles of Phaeocystis sp. Coiled filaments before release (top); star-like
configuration after release (bottom).
Dinophyta
The most common type of extrusomes, of almost universal occurrence in the motile phase of these
algae, are trichocysts, that is, rod-shaped bodies that, when mature, usually lie in the amphiesma
perpendicular to the cell membrane (Figure 2.84). The shaft is a paracrystalline, proteinaceous
rod a few micrometers long and rectangular in cross-section. At its distal end it extends as a
group of twisted fibers. The whole is enclosed within a membranous sac, and there is a sheathing
material between the rod and the membrane. The tip of the sac is in contact with the cell membrane,
passing through the amphiesmal vesicles, and the thecal plates, if present. Thrichocysts are formed
in the vicinity of the Golgi body and move to the cell periphery. They are discharged apparently by
a rapid hydration process, the discharged structures measuring up to 200 mm in length. Their func-
tion is unknown, but it is assumed to be defensive, excretory, or both.
