Caribbean Christmas tree worms (Annelida: Polychaeta: Serpulidae: Spirobranchus) are considered host generalists in their associations with anthozoan (Scleractinia) and hydrozoan (Millepora) stony corals. As planktonic larvae, they settle on coral surfaces and start secreting a calcareous tube to be used as a dwelling. This tube usually becomes overgrown by the host coral (except for its opening) and may get encapsulated deep inside the coral skeleton. In this manner, the well-protected worms grow and survive predation and other hazards, allowing them to live for over four decades. When the host corals are overgrown by other organisms, such as octocorals and sponges, these may act as secondary hosts.
The long lists of Caribbean host species suggest that the recorded number has reached a maximum. However, recent surveys (2015–2019) in the southern and eastern Caribbean, as well as in the Greater Antilles, enabled us to establish new records of two primary hosts (scleractinians) and two secondary hosts (a zoantharian and an ascidian).
Article referenced in BioNews 34 article "New discoveries on relationships between host corals, crabs and christmas tree worms"