Complex sentence: Reproduction occurs in midsummer, when the warmer water temperature and lunar cycle among other factors triggers sexually mature worms to transform into non-feeding stage called Epitoky with enlarged parapodia and swim to the surface of the water where both sexes release gametes, and then die.
Split into simpler sentences: Reproduction occurs in midsummer, when the warmer water temperature and lunar cycle among other factors triggers sexually mature worms to transform into a non-feeding stage called the epitoke. With enlarged parapodia, they swim to the surface of the water where both sexes release gametes, and then die.