Gonophore

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 gone (that which produces seed) and phoreus (bearer).

Gonophores are borne on branching stalks that grow out as a ring from the hydranth (i.e. the hydroid polyp, bearing a mouth, digestive cavity and tentacles) wall. The germ cells are formed from the inner layer of the entocodon. The entocodon is the primordium (i.e. the first cells that give rise to the development of an organ) of the subumbrella ( i.e. the concave oral surface of a medusa) 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 (= i.e. belonging to a hydroid perisarc) gonotheca. Medusae forming on fully developed hydranths are extremely rare; usually the gonophores develop into medusae or into sessile sporosacs.

The gonophores in the superfamily Plumularioidea are usually fixed sporosacs (i.e. gonophores held in place and not released into the water during larval development), more rarely they are rather reduced medusoids.

The gonophores in the family Lovenellidae are pedunculate free-roaming medusae.

The gonophores in the family Haleciidae are typically sporosacs, growing singly 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 (i.e. the living axial portion of a modified gonangium, from which numerous medusae are budded.) 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.

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