A gonophore is a reproductive organ in Hydrozoa that produces gametes. It is a sporosac, a medusa or any intermediate stage. The name is derived from the Greek words γόνος and -φόρος. Gonophores are borne on branching stalks that grow out as a ring from the hydranthwall. The germ cells are formed from the inner layer of the entocodon. The entocodon is the primordium of the subumbrella in the development of medusae from the gonophore. The gonophores in the order Leptomedusae are borne on much reduced hydranths and are usually protected in a peridermal gonotheca. Medusae forming on fully developed hydranths are extremely rare; usually the gonophores develop into medusae or into sessile sporosacs. The gonophores in the superfamilyPlumularioidea are usually fixed sporosacs, more rarely they are rather reduced medusoids. The gonophores in the family Lovenellidae are pedunculatefree-roaming medusae. The gonophores in the family Haleciidae are typically sporosacs, growingsingly or bunched into a glomulus. They remain attached to the hydroids or break off to be passively drifted away; in a few, the gonophores are naked. The gonophores in the family Sphaerocorynidae are borne singly or on short, branching blastostyles between or below tentacles. They develop into free medusae or eumedusoids. The gonophores in the family Corynidae are borne on hydranths and either liberated as free medusae or retained as medusoids or sessile sporosacs. The gonophores in the family Hydrocorynidae are borne in clusters on proximal part of hydranth body or develop from hydrorhiza. The gonophores develop into free medusae or sessile sporosacs. The gonophores in the family Candelabridae are fixed sporosacs. They develop on the aboral part of the hydranth below the tentacle-covered region, either directly on the hydranth or on spindle-shaped blastostyles. The gonophores in the family Tubulariidae develop above the aboral tentacles and develop into free medusae or fixed sporosacs The gonophores in the family Corymorphidae are borne above aboral tentacles, either directly issuing from hydranth wall or on blastostyles. The gonophores develop into free medusae or fixed sporosacs. The gonophores in the family Tricyclusidae are fixed sporosacs, with only male specimens observed. The gonophores in the family Pennariidae develop above the aboral tentacles. They may or may not liberate eumedusoids. The gonophores in the family Cladocorynidae are carried singly or on short, branched pedicels on the lower or middle part of the hydranth. They developing into free medusae or fixed sporosacs. The gonophores in the family Solanderidae, where known, arise directly from coenosarc. They are cryptomedusoid or eumedusoid. The gonophores in the family Milleporidae arise from the coenosarc within chambers embedded entirely in the coenosteum.
