protozoa: [19] Greek prótos meant ‘first’ (like English first and Latin prīmus ‘first’ it goes back ultimately to Indo-European *pro ‘before, in front’). It forms the basis of a wide range of English words, both original Greek compounds and post-classical formations, among them protagonist [17] (etymologically the ‘first or leading actor’), protein, protocol, proton [20], protoplasm [19], and prototype [17]. Protozoa itself was coined in modern Latin by the zoologist Goldfuss in 1818 from proto- and Greek zóia ‘animals’ (source of English zoo), the notion being that the protozoa are the simplest or most primitive forms of life. => zoo
1828, from Modern Latin Protozoa, coined 1818 by German zoologist Georg August Goldfuss (1782-1848) from Greek protos "first" (see proto-) + zoia, plural of zoion "animal" (see zoo). Originally including sponges and corals; current sense is from 1845. Related: Protozoon (aingular); Protozoan.
