Epitoky

[1] Unlike the immature form, which is typically benthic (lives on the bottom), epitokes are specialized for swimming as well as reproducing.

Many genetically identical epitokes are formed in this way, thus allowing a higher chance of finding a mate of the same species and subsequent passing of genes to the next generation.

Modifications may include an increase in size of parapodia and the development of paddle-like chaetae for enhanced swimming ability, atrophy of the gut, filling of the body cavity with gametes (eggs or sperm), the development of large eyes, and the musculature may even change to perform swimming movements instead of feeding movements.

[2][3] The majority of species that undergo epigamy are unable to revert to the atoke form and die after reproducing.

Male and female epitokes are produced and swim to the water's surface only at certain times of the year and are often synchronized with moon cycles in a behavior called swarming.

Syllid polychaete budding epitokes for the purpose of sexual reproduction.
Alitta succinea (common clam worm) in epitoky stage
Atoke of Platynereis dumerilii : It is yellowish-brown
Female epitoke of Platynereis dumerilii : Its body is filled with yellow eggs.
Male epitoke of Platynereis dumerilii : Its frontal part is filled with white sperm, while its rear is red due to blood vessels.