As nouns the difference between coelenterate and protozoan

is that coelenterate is any simple aquatic animal bearing tentacles with nematocysts. Examples include jellyfish, coral, and anemones while protozoan is any of the diverse group of eukaryotes, of the phylum Protozoa, that are primarily unicellular, existing singly or aggregating into colonies, are usually nonphotosynthetic, and are often classified further into phyla according to their capacity for and means of motility, as by pseudopods, flagella, or cilia.

As an adjective protozoan is

of, pertaining to, or characteristic of a protozoan.