Difference between protozoa, protists, protoctista?

Question

Are protozoa, protists, protoctista different classes of organisms or simply different names for the same?

Answer 1

Protists, also referred to as protoctista, is one of the six kingdoms. Protist has been used to describe the single celled organisms of the kingdom while protoctista has been used to include the multi-cellular organism. It is common to use just protist to describe the kingdom, including both single and multi-cellular organisms. A protozoa is a type of protist.