Mass spawning after the full moon.
Cephala is a phylum of parasitic worms that have an elongate sac-like body, no internal alimentary canal, and use a spiny protrusible proboscis for attachment to the intestinal wall and a mass of pinnate (feather-like) tentacles borne at the anterior end of many species. Although, parasitic in nature, they've evolved to survive outside their host's gastrointestinal systems.
These species have a varied sex life. They are simultaneously male and female (hermaphrodites) and typically pack both eggs and sperm (gametes) into tight bundles that are released after dark with remarkable synchronization. The bundles float in the air and open, allowing the eggs to meet compatible sperm.
Less commonly, this species assumes separate sexes when colonies breed outside of their hosts, whereby one aggressive and dominant worm becomes male and grows to an incredible size, influencing the rest of the colony to become female, fertilizing the entire colony.