Which organism is not considered a parasite?

Ringworm is classified as a fungal skin infection and is not a parasite in the same way that tapeworms, roundworms, and flukes are. It is caused by fungi that live on the skin, hair, or nails, rather than by organisms that exploit a host's resources and often live within the host's body. The organisms listed in the other options—tapeworms, roundworms, and flukes—are all types of helminths, which are parasitic worms that depend on a host to survive and reproduce. They invade their host's body and derive their nutrition from the host, which distinguishes them clearly from fungi like ringworm that can survive independently within the environment.