Gonozooid is a zoological term applied to animal species that practice alternation of generations, in which a particular class of generation performs the functions of sexual reproduction. A gonozooid typically has hardly any other function than reproduction, amounting to little more than a motile gonad. The best-known examples among the Animalia occur among the phyla Cnidaria and Bryozoa, and the subphylum Tunicata.
The production of gonozooids amounts to one aspect of certain classes of alternation of generations. In biological terms the various forms are examples of evolutionary strategies and are largely analogous rather than homologous; the gonozoid phases of say, the Tunicata did not evolve from anything like say, a Bryozoan.