Each of the over 80 families living today have characteristic body shapes and chaetal types. The families include for example centipede-like free-living crawlers like the nereidids and phyllodocids, colonial reef-building static forms with fans of head tentacles like the serpulids and sabellariids, flattened worms protected with shield-like dorsal scales like the polynoids, and predatory swimming worms with giant eyes like the alciopids. There are polychaetes specialised in many other unique ways, including in the ways they reproduce. Notably most Syllidae, Nereididae, and some Eunicidae (Palolo worms) metamorphose to become night-time swimmers to meet their mates, with timing of swarmings synchronised with the phases of the moon.