Fig. 1.

Geographical origin and life cycle diagram of T. rubra (Left) and T. dohrnii (Right). Light blue arrows indicate the typical life cycle while dark blue indicates the alternative ontogeny reversal of T. dohrnii. In this process, the free swimming medusa shrinks until the cyst stage, where all structures from the medusa totally disappear into a homogeneous opaque mass. Later, a stolon starts growing from the cyst and polyp buds appear to become fully grown polyps afterward.