Final answer:
Flukes are parasitic flatworms that attach to and infect internal organs of their host, including the liver and intestines, and can cause serious diseases such as schistosomiasis.
Step-by-step explanation:
Flukes are parasitic flatworms that infect the internal organs of their host. These organisms, known as trematodes, have a leaflike appearance and are equipped with an oral, and sometimes a ventral as well, which they use to attach to the inner walls of the host's intestines, lungs, blood vessels, or liver.
Trematodes exhibit complex life cycles that typically involve multiple hosts, with the primary host usually being a vertebrate and the secondary host often being a mollusk. In humans, they are capable of causing serious diseases such as schistosomiasis. For example, liver flukes (e.g., Clonorchis and Opisthorchis) and the oriental lung fluke (Paragonimus westermani) are well-known examples of flukes that can cause significant health issues.