The armour-plates are often exquisitely sculptured, and may be produced into spines or perpendicular plates to give greater surface extension, as we find in other plankton organisms. The cortical plasma may protrude pseudopodia in the longitudinal groove; it contains trichocysts in several species, true nematocysts in Polykrikos. [Please select]
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The "trichocysts" of certain protozoa bear a certain resemblance to the nettle-cells of coelenterates and probably have similar functions. [Please select]
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