How can parasitic isopods change the bodies of their crustacean hosts?

Parasitic isopods can significantly alter the bodies and biological characteristics of their crustacean hosts. When these parasites infect a host, such as a decapod, the body of the host may become notably deformed.1

Furthermore, the parasitic female isopod itself undergoes a dramatic transformation, becoming highly specialized and appearing quite different from the smaller, symmetrically segmented, and free-living male. In some instances, parasitism can also lead to hormonal alterations that affect the host's sexual characteristics. For example, when a male crab is parasitized, it may increasingly resemble a female at each molt, a process of feminization that occurs even if the crab's testes remain unaffected.12