Figure 30.20 Nematocysts Are Potent Weapons (A) The tentacles of the Portuguese man-of-war, a hydrozoan, are rife with specialized cells called cnidocytes. These cells contain stinging organelles called nematocysts, which inject toxins into their prey. The Portuguese man-of-war is a colonial organism, composed of many physiologically integrated individuals with specialized functions. (B) Nematocysts of the Portuguese man-of-war cause painful reactions when they come into contact with human skin.