||Areas dominated by mound-like, bush-like, or patchy growths of living Serpulid worms
that have secreted tubes of calcium carbonate to form complex aggregated structures.
Serpulid worms can be distinguished from Sabellariid worms (see above) by the presence
of a hard operculum that seals the hard, shell-like Serpulid tube. Living Serpulid
reefs are extremely rare in U.S. coastal waters, but recently extinct Serpulid reef
structures do occur, e.g., in certain Gulf of Mexico embayments. If no living Serpulid
worms are present and the reef is extinct, it is classified in CMECS as Substrate
(see Section 7.4.2). Living Serpulid reefs are, however, found in other parts of the
world, and are considered valuable structure-forming habitat.