Page 143 - Algae

126 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 2.83 Ejectile organelles of a cryptophyte. Discharging ejectosome (left) and reel of an undischarged
ejectosome just begining to be pulled out (right).

A less ordered type of extrusomes in dinoflagellates is the mucocyst, a simple sac with granular
content, associated with the release of mucoid material. They are located just beneath the cell mem-
brane, and are often aggregated in the region of the sulcus; their release in some species is corre-
lated with the psamnophilous existence of these algae, facilitating the attachment of the cells to
sand grains along the seashore.
More elaborate extrusomes termed nematocysts are found in genera such as Polykrikos kofoidi
and Nematodinium; usually only about eight to ten nematocysts are present per cell. These orga-
nelles are larger than trichocysts and can reach 20 mm in length. They are conical, fluid-filled
sacs with a capitate blunt end. Most of the body consists of a large posterior chamber, from
which a smaller anterior chamber is isolated; the whole structure is capped by a lid-like operculum.
A sharp stylet in the anterior chamber is connected to a tubular filament in the posterior chamber
(Figure 2.85).