Gonophore

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Gonophore

What is it
A gonophore is a reproductive organ found in hydrozoans (a group of small aquatic animals). It makes gametes (sperm or eggs). It can appear as a sporosac, a medusa, or an intermediate form.

Where it sits
Gonophores grow on branching stalks that extend from the hydranth, the feeding polyp of the colony.

How it develops
The germ cells come from the inner layer of the entocodon, the early tissue that forms the subumbrella (the inner, concave surface) of a medusa as it develops from the gonophore.

Diversity in form
Gonophores vary a lot among hydrozoans. They may be:
- Fixed in a protective covering (a perisarc coat called a gonotheca) or develop into free medusae.
- Born on different parts of the colony, such as hydranths or hydrorhiza (the stalk of the colony).
- Seen as fully formed medusae, or as sessile (non-moving) sporosacs, or other intermediate forms.

Examples (group differences)
- Leptomedusae: gonophores on reduced hydranths, often protected inside a gonotheca; medusae are rare but can form.
- Plumularioidea: usually fixed sporosacs; sometimes reduced medusoids.
- Some families have pedunculated (stalk-bearing) free medusae.
- Other groups may produce medusae directly, or remain as sporosacs attached to the colony.

In short
Gonophores are the flexible, varied reproductive structures of hydrozoans that produce gametes, appearing in many shapes from fixed sacs to free-swimming medusae.