As nouns the difference between sponges and protozoan
is that sponges
is plural of lang=en 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 a verb sponges
is third-person singular of sponge.
As an adjective protozoan is
of, pertaining to, or characteristic of a protozoan.