Abstract: Some rotifers of Monogononta can quickly produce morphological defenses under different environmental factors, and the generation of defense is the essential protection strategy in a changing environment. In the presence of environmental factors, rotifers respond with morphological defenses such as longer or shorter spine, larger or smaller body, and thicker lorica. This essay categorizes rotifer defensive morphological changes and summarizes environmentally induced factors including kairomone, temperature, food deficiency, and other internal factors. We then discuss the fitness benefits and costs of the morphological responses.