Affixes

Examples of this ending include bryozoon (Greek bruon, moss), a group of sedentary aquatic invertebrates that comprises the moss animals; protozoon (Greek prōtos, first), a single-celled microscopic animal, such as an amoeba, ciliate, or sporozoan; spermatozoon (Greek sperma, spermat‑, seed), the mature motile male sex cell of an animal, by which the ovum is fertilized.

A common plural for these is ‑zoa (bryozoa, spermatozoa); this ending also occurs in the taxonomic names for some groups of animals, of which examples include Anthozoa (Greek anthos, flower), a large class of sedentary marine coelenterates that includes the sea anemones and corals, and Hydrozoa (Greek hudōr, water), a class of coelenterates which includes hydras and Portuguese men-of-war.

Forms in ‑zoan are primarily adjectives, but can also act as nouns; as nouns, they are sometimes more common than the alternatives in ‑zoon: bryozoan, hydrozoan, protozoan.

Adjectives relating to these and other types of animal are formed using ‑zoic: cryptozoic (Greek kruptos, hidden), relating to small invertebrates living on the ground but hidden in the leaf litter, under stones or pieces of wood; also epizoic, hydrozoic, protozoic and others. For the names of geological periods in the same ending, see ‑zoic¹.