Mastigophore and Protozoan

Mastigophore noun - A usually nonphotosynthetic free-living protozoan with whiplike appendages; some are pathogens of humans and other animals.

Protozoan and mastigophore are semantically related. In some cases you can use "Protozoan" instead a noun "Mastigophore".

Protozoan noun - Any of diverse minute acellular or unicellular organisms usually nonphotosynthetic.

Mastigophore and protozoan are semantically related. Sometimes you can replace term "Mastigophore" with "Protozoan", this nouns are similar.