How do polychaetes reproduce in ocean water?

Most polychaetes reproduce sexually with separate sexes, typically by discharging eggs and sperm directly into the ocean water, where fertilization occurs externally.12

To facilitate this, many species undergo a transformation into a specialized reproductive form called an epitoke. At specific times—often synchronized by lunar cycles—these epitokes swarm to the ocean surface in large numbers. This process is highly coordinated:324
* Chemical Signaling: In some species, such as clam worms, females release a chemical substance called fertilizin that attracts males and stimulates them to shed sperm. The presence of sperm in the water then triggers the female to release her eggs.342
* Visual Displays: Some polychaetes use bioluminescence to attract mates and aid in species discrimination.3

Following fertilization, the resulting embryos typically develop into free-swimming, ciliated trochophore larvae. While this is the standard method, some species exhibit variations, such as brooding their young or producing egg capsules, particularly if they lack a pelagic larval stage.51