While some of the species are bisexual, others are protandrous, self-fertilizing hermaphrodites.
A few species, however, are bisexual, e.g.
Spikelets bisexual, or male and bisexual, each male standing close to a bisexual.
Hydra is, moreover, bisexual, in contrast with what is known of hydroid colonies.
Both male and female gonoducts open through acornmon atrium to the exterior by tkis pore, but in three bisexual genera the male and female ducts are developed in separate individuals (Bilharzia, Didymozoon, Koellikeria).